SECTION III.FUNGI.
TheFungi are enormously numerous. No less than 2,000 of the highest and most conspicuous of these plants have been figured; many more have been described; multitudes of those inhabiting the torrid zone are unknown; and the microscopic and parasitic tribes are innumerable. Though with a few exceptions entirely formed of cellular tissue, the fungi resemble animals in respiration and chemical constitution. They contain more azote than any other of the Cryptogamia, and obtain it chiefly from their food, which consists of animal and vegetable substances alive, dead, or decomposed. They inhale oxygen, and exhale carbonic acid gas, so that they never form true chlorophyll. No plants are more dependent on heat and moisture; many perform all the functions of life and reproduction independently of light, preferring dark and shady places to sunshine.
The Fungi form two principal groups, distinguished by their mode of fructification. In the higher group,Sporiferi, the fungus produces naked spores either single or compound, by means of which it may be multiplied. In the lower group,Sporidiiferi, the fructification consists of sporidia, enclosed in a distinct sac. The Sporiferi include the following orders, Hymenomycetes, Gasteromycetes, Coniomycetes, and Hyphomycetes. The Sporidiiferi include the Ascomycetesand the Physomycetes. These various groups we may now proceed to examine.
The most important family of Fungi is, without question, that of theHymenomycetes, the species of which far excel all others in their richness of colouring, and beauty of form. In this group the hymenium is free and mostly exposed. It comprises six orders, of which the Agaricini hold the first place. The genus Agaricus alone comprises 1,000 distinct species, which assume as many different forms and colours, with only slight modifications of substance, and it surpasses in number of species all the other generic groups known.
The Agaricus campestris, or common mushroom, is a type of that vast group; it consists of two distinct parts, the nutritive and reproductive. The nutritive part is the mycelium or mushroom spawn of gardeners, which resembles a mass of white spider’s threads mixed in inextricable confusion, and carries on for a time all the functions of the plant. Mycelia may exist for years without bearing the reproductive part, but fruit never can be produced without spawn. The mushroom itself, which springs from the spawn, is the fruit-bearing part, in which the spores are formed and ripened. It is distinguished by a kind of hat or bonnet called the pileus, supported by a stem. The pileus is lined by a number of gill-shaped plates or lamellæ radiating from a common centre; they are the reproductive organs in which the spores are produced by free cell formation, a process always preceded by a concentration of the matter within the parent cell, which is then divided into as many nuclei as there are to be spores. In the higher fungi, the number of spores thus formed is definite; in the Agarics they are in groups of four placed at the extremity of a stem, springing from the summits of these reproductive gills. Most of the Agarics rise from theground without any cover; the pileus or cap may show every variety from a smooth polished surface to hairs or shaggy scales, but some of the more highly organized have a general wrapper or volva, which encloses the whole plant, and bursting at last, it leaves some traces behind. In others, the pileus is at first clothed with fibres, which vanish or leave traces on its margin forming a veil or curtain. Some have a membrane attached to the stem, either connected with the volva, or spread under the gills when young, and, when more or less persistent, it is called a ring.
The spawn, which is the earliest product of the spore, has a great variety of forms. Sometimes it is filamentous, sometimes tubular, creeping extensively, or concentrated in a felted mass, sparingly developed, or produced in abundance. Besides, it is developed in a great variety of situations often difficult to detect. The fructification is alone evident, under innumerable forms, which are as rapid in their growth as they are for the most part ephemeral in their duration. Some species have been known to acquire several square inches of surface in a single night; the plant, however, is often far advanced before it appears above ground. Some Agarics grow most readily after thunder storms and abundant rains; certain species are always single; others grow in dense aggregations; while in several species there is a tendency to assume a circular arrangement, and that not merely when the spawn is perennial, but when the whole existence of the fungus is confined to a few days or weeks.
A mass of spawn is not always produced by a single spore, but by a collection of spores, from whence it spreads in every direction, and forms a common belt. In the Agaricus arvensis, Marasmius Oreades, &c., it spreads in a circle and bears fruit; and, as it continues to spread, the same process takes place at each circumference. In this way are formed the Fairy Ringsso frequently seen in pasture lands. The fairy rings are sometimes of very ancient date, and attain enormous dimensions, so as to be distinctly visible on the side of a hill from a considerable distance. It is believed that they originate from a single fungus, whose growth renders the soil immediately beneath unfit for its reproduction. The spawn, however, spreads all around, and in the second year produces a crop, whose spawn spreads outwards again, for the soil behind forbids its return in the opposite direction. Thus the circle is continually increased, and extends indefinitely till some foreign cause destroys it. The manure arising from the dead fungi of the former years makes the grass vigorous around, so as to render the circle visible even when there is no external appearance of the fungus; and the contrast is often the stronger from that immediately behind it being killed by the old spawn. This mode of growth is far more common than it is supposed to be.
The depth to which spawn penetrates and the rapidity of its growth even in the hardest timber if exposed to damp is quite astonishing. Instances occur in which the spawn of dry rot not only enters wood, but penetrates solid structures of brick. It overcomes an immense resistance.
The genera of the Agaricini differ in substance; some are almost ligneous, others leathery or tough, occasionally they are delicate and deliquescent, and although most of them are entirely formed of cellular tissue, the Lactarii and Russulæ form remarkable exceptions in having laticiferous vessels mixed with their cellular structure. These vessels exist in all parts of the plants, especially in the gills, where they give out the liquid on the slightest touch. In the Russulæ it is watery; but in the Lactarii, in which it is either mild or acrid, according to the species, it is also of different colours, which sometimes change their tint upon exposure to the air,probably from ozone. In all fungi there is a small amount of poisonous matter, and the quantity in any given species is extremely uncertain, so that the same fungus which may be eaten with safety in one country, is deleterious in another.
In the dark coal mines at Dresden, luminous Fungi cover the roof and pillars with the most dazzling phosphorescent light, which increases with the temperature of the mine. Agaricus Gardneri, a species parasitic on the Pintado palm in Brazil, is highly luminous; and the Agaricus olearius in the south of France also possesses that rare quality. The gills under the pileus shine as brightly as a glow-worm, in the dark crevices of the olive stems in November and December. M. Tulasne found that the light was extinguished in vacuo or non-respirable gases, whence he concludes that it is due to a slow combustion without heat, arising from a chemical combination of the oxygen of the atmosphere, inhaled by the fungus, with a substance peculiar to the plant.
In a few Agarics the cells are so connected by veins or lateral branches, that they assume the character of pores, as in the Chantarelle, a sweet-scented lemon-coloured fungus, whose gills pass into mere veins, and its inferior fruit-bearing surface is all but even and uniform, so that it forms a connection between the Agarics and the Polyporei, a most extensive order of the higher fungi, essentially distinguished by having a multitude of pores in the smooth under-surface of the pileus, instead of gills. The pores are generally small; in some species they are hexagonal, and so large that they look like a honeycomb. In all, they are the mouths of cellular tubes, packed closely together side by side, or more closely connected, sometimes easily separated, sometimes inseparable. They constitute the fructiferous surface or hymenium of the fungus, and contain the spores. This structure gives the pileus a thick heavy appearance,and a vast variety of characters; besides, the substance itself varies in density and colour. The stem also may be long or short, sometimes wanting altogether, when the pileus or cap is attached to the surface on which the fungus is growing. The growth of individual fungi, whether Polyporei or Agarics, is centrifugal, that is, they spread from the centre of the pileus, as in the Polyporus fraxineus, which involves every stick and blade of grass it meets with as it increases in diameter, and continues to increase for years, till it is occasionally a yard across.
The fructiferous surface in the higher fungi is essentially turned away from the light, yet, although in many of the lower Agarics it is uppermost and exposed, such is the tendency to produce the fructification on the lower side, especially in the Polyporei, that if the position of the plant be reversed the hymenium or fructiferous surface is gradually obliterated and a new one is formed on the other side.
The Polyporei abound in the tropical forests, but species are found in all latitudes. The higher fungi are more or less plentiful in forests everywhere, and every genus of trees seems to have one or more species of fungus peculiar to itself. The Boleti, a genus of the Polyporei, which are thick fleshy fungi of various forms, and for the most part brilliantly coloured, grow under trees in the temperate zones, sometimes in conspicuous circles. When a slice of the Boletus luridus, cyanescens, or other species is exposed to the air, the white fleshy part acquires a blue tint in consequence of the action of ozone upon the acetate of aniline, which was ascertained by Dr. Phipson to be a constituent of these fungi. According to M. Dutrochet more heat is evolved by the Boletus æneus than by any other vegetable except the Arum.
The Polyporei destroy decaying trees and timber,and the Merulius lacrymans or common house fungus, attacks and induces the decay of timber previously sound. The cap is large, fleshy, spongy and moist, but delicate and velvety on the under-side, with wide porous dentate folds. The plant is yellow with a white woolly margin. It grows in a circle, and its mycelium attracts moisture from the atmosphere, which falls down in drops from the pileus. The decay of wood induced by the attacks of this mischievous fungus, is what is called dry rot.
The four principal sub-orders of the Hymenomycetes, or highest fungi, have a cap or pileus, and an inferior fructiferous surface characterized by gills, pores, or tubercles, and are connected by intermediate species; but the other two sub-orders are quite different. The Clavariei are club-shaped, upright, branching fungi, with the fructification surrounding the uppermost extremity of some of the stems. The finest species grow in the Swiss forests where they form an article of food; some are edible in Britain, but of smaller size.
The Tremellini consists of plants forming a gelatinous mass of a bright orange, purple, or dark brown colour, which may be seen on rotten sticks in hedges, and in enormous masses resembling the convolutions of an animal’s brain on the stumps of dead trees, or at the base of living ones. They are mostly plants of temperate climates, but the Exidia Auricula Judæ, or Jew’s ear, is universal. All fungi have a mycelium, but in this order it is not apparent. The structure of the fruit, as determined by the microscopic observations of Mr. Berkeley and of M. Tulasne, is unusual. The fructiferous part is very extensive, being uppermost and spread over the surface of the gelatinous mass, so as to follow all its inequalities. Threads rise from this fructiferous surface bearing on their extremities globular cells exhibiting a concentration of coloured matter generally divided into four lobes, and from the upper surface of theseglobular bodies, a number of flexuous threads spring, carrying on their tips cymbiform spores.[52]
In the preceding family (Hymenomycetes) the fruit-bearing surface has free access to the air, but in the group of theGasteromycetes, which consists of five or six sub-orders, it has neither access to air or light till the fruit is ripe, for the fructification is enclosed in a rind of one or two coats, and springs without a stem from a gelatinous thready, or cellular mycelium. The most important group, Trichogastres, includes the puff-balls, which grow on the ground. Of these the Lycoperdon, found everywhere on pasture grounds and meadows, is a familiar instance. When young it has a milk-white coat filled with closely packed cells, some of which bear naked spores set upon spicules. When mature, the whole of the interior vanishes, leaving nothing but a mass of threads and fruit; the coat becomes brown, bursts open at the top, and gives vent to a cloud of microscopic spores like the finest dust. In general the ball is sessile, or it has merely the rudiment of a stem. The Lycoperdon giganteum, an exceedingly large species, is a native of a warm climate. The tops of some of the branched threads of its hymenium swell into pear-shaped cells surmounted by short spicules ending in spores; when young it is edible, when dry it is used for tinder and as a styptic, and when ignited its fumes possess a property similar to that of chloroform. The Batarrea forms a contrast to the common puff-balls, being mounted on a stem sometimes a foot and a half high. It has several coats enclosing a thick gelatinous substance in which the threads carrying the spores are distinctly spiral and closely twisted.
The sub-order Hypogæi is subterranean, as the nameimplies. The exterior coat of these fungi is inseparable from the internal matter, which is for the most part fleshy. In some species it is dry, in others it abounds in milky juice; but in all the fruit is formed in hollows excavated in the interior mass. In some species these cavities are traversed by threads, and in many species the spores accumulate in such multitudes within the cavities, as to make it certain that the spicules, on which the spores are borne, produce successive crops. They are set free by the rupture of the rind. A species of the genus Melanogaster, abundant in the south of England, is edible and sold as the red truffle of Bath; but it is far inferior to the real truffle.
The order Phalloidei has a club-shaped or globose head, composed in the interior of large cells mixed with fruit-bearing cavities. This head has a coat consisting of a jelly inclosed between two heterogeneous strata. The whole interior of the fungus deliquesces, changes to a mucilage, and drips out of the exterior coat in drops dark with microscopic spores. The colour of these fungi is often beautiful, but their smell is most loathsome, tainting the air to a considerable distance; yet the gelatinous volva of more than one species—an Ileodictyon—is eaten by the New Zealanders under the name of thunder dirt, and Phallus Mokusin is an article of food in China.
Certain species of these fungi have a rudimentary stem in their early stages, but it becomes full of deep pits or cavities and suddenly acquires an enormous development when the plant approaches maturity. The cavities are at first strongly compressed, but as the stem increases, they acquire a rounder form, till at length their vertical tendency is so strong that the coat or volva of the fungus is ruptured, which could only be effected by a very strong force. Moreover, the stem is fixed to the base by so small a point that the plantcould not remain erect were it not for the tubes of the volva which contract on the stem and act as a sustaining force. Thus these very revolting fragile plants afford a very striking instance of mechanical power exerted by vegetable matter.
The Myxogastres are an anomalous group of fungi which often appear as black or coloured spots on dead leaves and twigs. Sometimes their mycelium or spawn is large and conspicuous, as that of the Reticularia maxima, which overruns cucumber beds, choking up the breathing pores, and killing the plants. Species of these fungi are found upon mineral and vegetable substances dead and alive, and the same species grows upon plants of very different affinities, so that they depend upon the atmosphere for their nourishment, and not on their matrix. Like the puff-balls they end their lives in myriads of microscopic dust spores, but they begin it as a gelatinous mass, sometimes sparkling as a gem, brilliant with the metallic tints of gold, silver, steel, or copper.
The gelatinous or creamy mucilage of which these fungi consist, forms a mycelium which is either diffuse, or creeps over the matrix on which it grows in anastomosing filaments like a network, or it is arranged without any definite order. This spawn gives rise to many bodies having an envelope of one or more concentric membranes, technically called a peridium, enclosing a gelatinous fertile substance which, when mature, becomes a mass of scales or threads mixed with spores; the spores are mostly attached to short threads singly or in groups, sometimes surrounded by a firm coat or cyst. These bodies are either sessile on the mycelium or stalked, and are either free or confluent. In their soft state the tissues are so delicate that they exhibit no structure, but just as they are passing from the puffy to the dry dusty state there are indications of it.
It would be tedious to describe the variety of forms assumed by the fruit-bearing bodies in the different genera of these fungi, or the manner in which they are ruptured to give egress to the spores, which differ in colour according to the species, though they are for the most part red. The forms of the chaffy scales and threads are equally diversified: in the species of Trichia, the threads contain one or more spiral filaments, a form peculiar to the vegetable kingdom.
Botanists are now generally of opinion that the Myxogastres are vegetables, although the singular Amœba-like motions some of them exhibit, and the nature of the motile bodies they produce, seemed to assign them a place in the animal kingdom; indeed, even now little is known of the reproduction and final life-history of these singular fungi.
Motions precisely similar to those of the Amœbæ, the lowest class of animal existences, were observed by MM. Hoffmann and Tulasne, and more especially by M. de Bary,[53]in the Æthalium septicum. It is a yellow pulpy mass, produced upon a spawn or mycelium consisting of semi-fluid gelatinous anastomosing filaments, often widely spread through the moist tan in hothouses.
M. de Bary describes the filaments of the mycelium as full of a multitude of small colourless corpuscles mixed with large yellow ones; moreover the branches of this mucous network are described as continually changing their form, in a manner closely resembling the pseudopodia of the animal Amœba. They push out new branches, others are withdrawn, and the whole mycelium frequently advances with a creeping motion of translation. The yellow pulpy mass produced by the mycelium is entirely composed of similarly constitutedsoft filaments about the thickness of a bristle closely interlaced. They anastomose in all directions, in long or short meshes, and their upper free extremities form groups of projections which bristle the exterior surface of the pulpy mass.
When that mass is about to form spores, all the asperities on its surface are withdrawn and replaced by a bright yellow network of irregularly interlaced filaments, which constitutes an envelope to the interior spore-forming part, consisting of a white central liquid or plasma containing an innumerable multitude of colourless granules. Both of these parts are formed at the expense of the filaments which are decomposed, the yellow granules are absorbed in the envelope, while the colourless granules retire with the gelatinous matter towards the centre to constitute the plasma, which is the fruit-producing part. Transparent globular cells containing nuclei are generated simultaneously in every point of the plasma, round each of which a portion of the granular matter is consolidated; it takes a dark purple colour and constitutes a spore, myriads of which, fine as dust, are thus generated. The whole of the plasma is consumed in the spores, except a very small quantity, which forms the threads found mixed with the spore dust. According to M. de Bary the complete development of the Æthalium, from the instant it appears above the tan in a hothouse of high temperature to the maturity of the spores, is accomplished in about fifteen hours. The rapidity of growth of this fungus is therefore astonishing. Mr. Berkeley mentions that a mass of it two feet long, formed of many confluent individuals, was formed upon a piece of iron that had been red-hot twelve hours before—a proof among many others of the meteoric nature of these fungi, the atmosphere affording them a sufficient supply of food.
The motions of the plastic matter contained within the dust-like spores of the Æthalium septicum exhibit amœban motions of the same character as its mycelium. For when M. de Bary placed ripe spores of that fungus in water, their skin burst open and the plastic granular matter was set free under the form of a coherent globular mass without any exterior membrane. These globular corpuscles exhibited amœba-like changes of form; processes were pushed out, and then drawn in, till at last they assumed an elongated cylindrical shape round at one end, prolonged at the anterior end into a long cilium with which they turned convulsively round their axis. At the same time vacuoles were frequently seen to expand and contract alternately in the round extremity. Ultimately these bodies lost their middle, and at last were divided into two equal parts, each of which went through the same changes as the primary globule, and at length assumed the ciliated active form. Besides these active bodies, there were others which never acquired cilia. The motile bodies were also discovered in other species of these fungi by M. Hoffmann; there can be no doubt that they are either zoospores, or of the same nature as the eel-shaped motile bodies in some of the Algæ; possibly the bodies which never acquire cilia may be germ cells. There is still much obscurity with regard to the Myxogastres, inasmuch as the origin of their mycelium is unknown, whilst in all other fungi mycelium or spawn are produced by the germination of the spores. The spiral vessels found in the threads of the Trichia prove that the members of this singular family are truly vegetables. Professor Fries places the geographical maximum or centre in the temperate zone, but different species are found from New Zealand to high northern latitudes.
The Nidulariacei constitute a beautiful order of thisfamily of fungi. The plants are exactly like a bird’s nest with eggs, sometimes with a stem, sometimes without. At first the nest or cup has a cover consisting of several coats, which either burst open with a stellate or irregular figure, or by the separation of a little lid; then the hollow of the cup or nest is exposed, and at the bottom are seen one or more sporangia, that is spore cases, often immersed in jelly and either free or fixed to the nest by an elastic string. The spore-coats at first contain a compact circular mass, but a cavity is afterwards formed in the centre, and the cells which terminate in the walls of the cavity bear spores on their tips. When ripe the spore cases are ejected by elastic power. The force with which the sporangium of the species of Sphærobolus is ejected, far exceedsin proportionthe force with which a shell is projected from a large mortar; this fungus sometimes grows in damp hothouses.[54]Many Nidulariæ are widely spread, but they thrive best in warm climates.
The intimate structure and fructification of the higher fungi are for the most part microscopic but an innumerable mass of the lower fungi are themselves invisible to the naked eye, living upon all kinds of vegetable and animal substances, dead, alive, fresh or putrid. They vegetate upon decayed linen, flannel, leather, and even on metallic and poisonous solutions. They yield myriads of minute spores wafted by every breeze. They float in the air we breathe, seeking a nidus in anything that will supply them with suitable food. There is scarcely a spot on the earth where these minute spores may not exist, and being insoluble, they wait where they fall for the growth or decay of the plant or animal which suits them. As parasites they are most destructive, producing disintegration, disease, and even death, both in vegetables and animals.
It is the mycelium or spawn which does the mischief, by supplying the fungus with food at the expense of the victim. The spores of the Botrytis Bassiana find a nidus in the breathing pores which open into the trachea of the silkworm; they develop their mycelium in the air-tubes, which are soon filled up; it then extends into the fatty matter under the skin, which nourishes the worm during its dormant state, and, as soon as that matter is exhausted, the victim dies.
In autumn, the common fly, though quite dead, may be seen adhering to many parts of a room, especially to the window glass, as if it were alive. In this state it is always surrounded by a halo about an inch in diameter of whitish dust, consisting of the spores of the Empusa Muscæ, or fly fungus. The body of the fly is much distended, the rings of its abdomen are separated by the growth of the mycelium from within, and all the contents of the body having been consumed by the parasite, nothing remains but a hollow shell with a thin felt-like layer of the interlaced mycelia of innumerable fungi, for the fly fungus increases with wonderful rapidity within the insect. Mr. Berkeley believes the fly fungus to be merely a condition or phase of one of those anomalous moulds which grow on dead fish, making them conspicuous as they float on the surface of the water, by the foggy halo which surrounds them. Different kinds of parasitic fungi may exist at the same time. Dr. Leidy found a variety in the stomach of the Passalus cornutus, a beetle that lives upon decayed wood. Fungi do not attack the carnivorous beetles.
Man is not exempt from these parasites. Fourteen different species of fungi were discovered by Mr. Hogg in as many cutaneous diseases. There cannot be the smallest doubt of cutaneous disease being induced by inoculation with fungi; merely rubbing certain specieson the skin is sufficient. Fungi cause baldness by fixing themselves on the roots of the hair, and destroying the internal structure of the bulb. Our eyes are not exempt from attacks of these parasites, for in performing an operation upon a diseased eye Dr. Hannover found several species of fungi in it; one of them was globular, and strongly refracted the light. There is a fungus consisting of from four to sixty-four cells united in square groups, which infests the stomachs of men and animals, even in a healthy state; but although fungi produce certain cutaneous diseases, there is no proof as yet that fever, cholera, or any other epidemic, is owing to the spores of the fungi which we inhale from the atmosphere.
The family ofConiomycetesconsists of six groups, two of which are parasites on living vegetables, the other four growing on those which are dead, decaying, or dying. They are microscopic plants, and their mycelium is filamentous, or vesicular, often obsolete; short threads rising from it bear on their tips either septate spores, or spores like fine dust, inclosed in oval or bottle-shaped cases, called perithecia, or in cells united in a cell, like a necklace of beads. We are chiefly indebted to M. Tulasne and his brother for the obscure and extraordinary life-history of these fungi.
The parasites on living plants form the two vast groups of Epiphytes and Entophytes. The Epiphytes exhibit their fructification on the surface of the plant, while their mycelium penetrates the moist texture of its interior, which feeds them. All parts are liable to be attacked by these fungi; they may insinuate their mycelium into the leaves, stem, flowers, stamens, anthers, and the very heart of the seeds. The mycelium is generally annual, but sometimes it is perennial, and leaves a crop of fungi year after year; it disintegrates thetissues of the plant on which it feeds, and distorts or kills it. Occasionally, the chlorophyll in the leaves is oxidized, and becomes yellow by the oxygen which the parasite absorbs.
The Entophytes, which constitute the second group of parasites on living plants, form microscopic congregations in the interior of the leaves and tender shoots, the only indication of their existence being a white, red, or orange coloured spot, which usually becomes black or brown when the fungus attains maturity. It appears that the same individual of these entophytes may assume two or more different forms during the course of its life, and bear two or more totally dissimilar types of fructification. Of these, the sub-orders Pucciniæ and Uredines furnish many examples.
Fig. 32. Pucciniæi:—a, Aregma speciosum;b, Xenodochus paradoxus;c, Puccinia Amorphæ;d, Triphragmium dubens;e, Young spores of an unknown Puccinia;f, Puccinia lateripes.
Fig. 32. Pucciniæi:—a, Aregma speciosum;b, Xenodochus paradoxus;c, Puccinia Amorphæ;d, Triphragmium dubens;e, Young spores of an unknown Puccinia;f, Puccinia lateripes.
Fig. 32. Pucciniæi:—a, Aregma speciosum;b, Xenodochus paradoxus;c, Puccinia Amorphæ;d, Triphragmium dubens;e, Young spores of an unknown Puccinia;f, Puccinia lateripes.
Fig. 32represents various species of Pucciniæi, which consist of a thread ending in club-shaped or elongated cells called asci, containing a definite or indefinite number of septate conidia or spore dust cells. Each order of plants, as the Rosaceæ, has its own form of these entophytes. In the tissue of a rose leaf, immediately beneath a bright golden coloured surface spot, M. Tulasne found two distinct forms of fungi, living together in a small cavity. The forms were exactly those of a Puccinia and Uredo. The Puccinia consisted of a short colourless stem, ending in a club-shaped cell, containingtwo conidia or spore cells. These fungi were crowded together in multitudes in a small space so as to form a solid rounded mass, with their broad tops immediately under the skin of the upper-side of the leaf, but sometimes they were arranged in concentric circles. The Uredines, on the contrary, had colourless branching stems, like threads, bearing on their tops pointed spore sacs. In some species these Uredines are scattered through the mass of Puccinia, in others disposed in a circle round it, or in the centre of the concentric ring where the Puccinia takes that form. It was long believed that these two forms of fungi living together in the same cavity were totally different plants, but as in various instances M. Tulasne perceived that the Uredo had sprung up, shed its spores, and vanished before its companion had ripened its fruit, he concluded that the two different forms are merely two states of the same plant, that the larger spores of the Uredo thus early matured, immediately germinate and produce the Puccinia, whose fine dust-like spores are merely the secondary fruit of the Uredo. These minute spores issue through a pore in the conidia or dust cell and a puncture in the upper skin of the leaf into the air, whence they are wafted in myriads by the winds; and, if not too late in the season, they enter into the pores of the leaves and tender parts of the same or other plants that may suit them, and within these they form a mycelium, and produce a young Uredo. Even if the autumnal leaves fall in a moist place before the spores have germinated, the entophyte will grow on the approach of spring, and ultimately send its dust spores to enter into young leaves, and grow with their growth.
Although there cannot be a doubt of the existence of the Uredines as a numerous natural family, M. Tulasne considers the species of certain genera to be only secondary forms of certain genera of Pucciniæ. Manyof these minute fungi have a third and even a fourth order of fruit; the principle being carried to a maximum in the order Cæomacei. These entophytes have a delicate mycelium, which gives rise to short or obsolete fertile threads, terminated by single spores or chains of spores. These spores when they germinate produce a second order of spores; these occasionally produce a third order, and so on successively even to a fourth or a fifth order. It is always the last and smallest spores which reproduce the plant. The object of the successive orders seems to be to diminish the size of the spores and to increase their number, that they may more easily enter the stomates of the plants they live upon, and be more easily and widely dispersed by the winds.
The Uredo candida, or Cystopus candidus, which takes its name from the white spot it forms on the leaves of the cabbage and other vegetables, is found to produce both female or germ cells and spermatozoids. Long before the white spot is formed on the leaf, the presence of the abundant spawn may be perceived by swellings and deformities in the victim plant. Its filaments, which creep exclusively in the intercellular canals of the cellular tissue, are tubular, of unequal diameter, and exceedingly branched, and are always formed of cellulose, either thick-walled and gelatinous, or thin-walled and membranous. From this mycelium, little threads hang down, ending in globular vesicles containing a nearly homogeneous colourless matter, and ultimately an aqueous liquid; they are supposed to fix the mycelium to the cells of the victim. According to the examination of Mr. Berkeley, M. Tulasne, and others, the branches of the mycelium accumulate in a hollow immediately under the white spot in the skin of the leaf of the plant attacked. From these branches spring bundles of club-shaped tubes, directed perpendicularly towards the upper skin of the leaf, and forming a tuft or little cushion ofvariable extent. The summit of each of these club-shaped tubes is formed into a conidium, or spore dust cell, which separates itself from that below it by taking a globular form. In the upper end of the remainder of the tubes, new spore dust cells are formed, and so on indefinitely. These conidia remain attached to one another in a string by slender constrictions which become thinner, and at last give way from above downwards, and they escape in succession through a crack in the skin of the leaf. The quantity of spores that are generated by the dense mass of these club-shaped tubes must be enormous.
The Cystopus has female reproductive cells, which had escaped notice from being hid in the plastic matter which nourishes them. They appear before the spore dust bearing cells, and are formed by terminal or interstitial swellings in the tubes of the mycelium, which become large oval cells, separated ultimately by a closure from the rest of the tube that bears them; they are filled with a granular liquid mixed with large granules of a coloured fatty matter. The tips of some branches of the mycelium swell into oval or club-shaped cells containing spermatozoids, which fertilize the female cells; then the matter within the latter assumes a globular form, gets a coat of cellulose, and becomes the true fruit of the Cystopus.
As early as the year 1807, M. B. Prévost had seen that the sporangia, or spore cells of the entophytes produced zoospores, and recently M. de Bary has seen them produced, during the germination of the spores, collected within a sporangium of the Cystopus. When they came into the water they had two cilia, one of which was short and went first, the other was long and trailed after the zoospore. Neither M. de Bary nor M. Tulasne have ever seen zoospores in the fungus itself, but if the drops of rain or dew round the white spot on theleaf of a plant be examined, empty sporangia are generally found, and spores in different states of development.
The Puccinia Fabæ, an entophyte on the common bean, has but one spore in its cylindrical case, and is considered identical with the Uromyces appendiculatus. Besides male organs like those of the Æcidium, M. de Bary found that the bean entophyte has four kinds of reproductive organs, of which one alone reproduces the original form, while the others present a well-marked alternation of generations. The Puccinia forms a prothallus on which conidia, or secondary spore dust cells, arise; these secondary spores form a mycelium, on which an Æcidium appears, whose orange-coloured fruit gives rise to a Uredo, and the dust spores of the Uredo enter the leaves of beans or peas, and grow into a Puccinia. All the species of Æcidium are similar to one another, and M. Tulasne is of opinion that they do not constitute a distinct genus, but that, like many of the Uredines, they are merely a secondary form of some other fungus, and inhabit the same cavity, as in the case of Æcidium cyparissiæ and Uromyces scutellatus, Æcidium leucospermum and Puccinia Anemones, and others.
Fig. 33. Puccinia Graminis.
Fig. 33. Puccinia Graminis.
Fig. 33. Puccinia Graminis.
The order Pucciniæi comprises epiphytes, as well as entophytes. The mildew on wheat is caused by the Puccinia Graminis (fig. 33), which attacks the stem of the plant, and appears on its exterior in a circular cluster of pear-shaped septate spore cases. These spore cases spring from a filamental mycelium, whose threads interweave themselves among the soft tissue of the stem of the wheat, and the fertile threads make their waythrough the stomates to the surface. Professor Henslow has proved that the rust which appears on the leaves and chaff scales of wheat is owing to the Uredo linearis, a secondary form of the Puccinia Graminis, and that rust is only an earlier form of mildew; so that the Puccinia Graminis is a dimorphous and epiphytic fungus. It may be a question whether the Uredo segetum, which destroys the blossom of wheat, and reduces the ear to the sooty mass of powder called smut, may not be the form of some other fungus. The epiphytes of the order Pucciniæi often appear on the exterior of plants in tufts of brown, yellow, orange-coloured, or white sporangia.
Fungi are extensively propagated by fragments of their spawn, and the threads of the mycelia are sometimes diminished in thickness in order that they may more easily penetrate into the stomates of the plant they invade. This was discovered by Mr. Berkeley while investigating the germination of the spores of bunt, a fœtid rust which attacks wheat and other grasses. It is perfectly analogous to the diminution of the size of the dust spores in the successive orders of fructification. It is thought probable that in many of the parasitic fungi, new spores are formed at the tips of the fructiferous threads of the mycelium as fast as the ripe spores fall off, whence that enormous mass of minute spores which a single individual is capable of producing.
Among the multitudes of known parasitic fungi, there is not one that does not form a mycelium more or less distinct. They do not arise from a disease in the plant they attack, though they ultimately cause disease and often death. Each parasite has its own mode of penetrating into the tissues, and its own manner of vegetating; they attack certain plants, and avoid others though nearly allied.
Dust spores, single or septate, oozing out of a dark or coloured fungous mass is characteristic of the groupMelanconiei, which is more remarkable in regard to the mode of fructification than any of the preceding Coniomycetes, for instead of successively assuming the form and fructification of two genera, or two orders, the plants successively assume the form and fructification of two distinct families.
The family of theHyphomycetestakes its name from its filamentous character. The mycelium gives rise to white, dark brown, or bright coloured threads, simple or compound, bearing naked spores on their extremities. Of these there are five sub-orders and many genera.
The sub-order Isariacei has four genera found on the pupæ of moths, on dead spiders, dead fungi, and dead plants respectively. The group is characterized by compound threads ending in pulverescent spores. Most of the caterpillars of the Bombyx Rubi, or bramble moth, fall victims to a species of Isaria, which has several distinctly different periods and modes of fructification, and at last assumes the form of a very beautiful fungus belonging to a different family.
Near Paris, in the month of October, when the caterpillars of the bramble moth seek for shelter from the cold, in the earth, or under long grass and withered leaves, M. Tulasne and his brother found that most of them were surrounded by tufts of a whitish down, which increased so rapidly that it killed the caterpillars and covered the whole of their body except the bristly hairs, and assumed characters similar to the muscardine fungus that kills the silkworm. This down is a mycelium composed of extremely fine branched filaments felted together, the upright fertile branches of which bear whorls of branchlets each terminated by chaplets of from ten to fifteen equal and spherical cells filled with dust spores. These most minute spores germinated, and put out filiform creeping germs which quickly emittedmany branches ending in long chaplets of fertile dust-bearing cells.
Points here and there on the felted envelope of the caterpillars became of an orange colour, took the form of a mycelium, and produced little orange coloured club-shaped cells which shed abundance of reproductive dust spores from a ring of white hairs on their summit. Each caterpillar had from ten to fifteen of these coloured clubs on its sides, which lost their brightness when they grew old, and had shed their dust spores. These fungi possessed all the characters of the Isaria crassa, or Isaria farinosa of Fries.
Later in the season other caterpillars on which this club-shaped Isaria had not been produced, but which were swollen and white with the felted spawn of the parasite, gave out orange red club-shaped vessels of a larger size and deeper tint than those of the nascent Isariacei. They had no terminal ring of hairs, but some of them had a red spore dust-bearing felt at their base. Ultimately they assumed all the characters of the Sphæria militaris of Ehrenberg or Cordyceps militaris of Fries, which is a bright scarlet fungus half an inch high with a fleshy upright stem ending in a cup-shaped head containing long cylindrical sacs called asci, in which the spore cells are so numerous as to resemble strings of beads.[55]This fungus, therefore, begins as a member of the family Hyphomycetes, and ends as a member of the family Ascomycetes.
The order Stilbacei are little globose fungi with or without a stalk, covered with semi-gelatinous spores. They are united in cushion-like masses, on decayed wood and dead twigs. The little scarlet masses on dead currant branches so often seen in gardens, are examples.
The order Dematiei are the black moulds found ondamp paper, old damp linen, dead wood and plants. Their spawn is seldom much developed, the fertile threads are erect, rigid, dark brown approaching to black, sometimes of an olive green. The spores on their tops are either simple, in whorls, or collected into heads, which are large, septate, and even spiral.
The Mucedines are beautiful microscopic objects both as to form and colour; they are very numerous both in genera and species and are well known as red, blue, or green moulds. These fungi spring from many points of a generally abundant mycelium, in erect coloured threads, bearing on their tips simple naked spores, spores collected into little tufts, or spores strung together like beads forming threads either branched or simple. In this order of fungi there are, moreover, instances of dualism, the second order of fruit being that of the family of the Ascomycetes.
The Botrytis, or Peronospora infestans, which causes the murrain in potatoes, shows how destructive the Mucedines can be. Like other entophytes, its spores enter the stomates in the leaves of the potato, and fill the cavities of the leaves with spawn, the ramifications of which are said to be very beautiful. This creeping spawn then insinuates itself into the stem and tuber, and from thence it finds its way to the exterior of the plant, or to some internal cavity, where it fructifies, bearing large globose sessile bodies yielding fruit of the second order, and spores on the tips of its fertile branches. The spawn of the Botrytis spreads rapidly in a circle, and soon destroys the texture of the leaves and stem, but although it attacks the tuber or potato generally so called, it does not penetrate deeply. The destruction of the potato is aided and completed by the Fusisporium Solani, a microscopic fungus, which takes various forms according to its age and changing conditions, the last of which seems to be partly gelatinous;it sometimes hardens the tissues of the potato, but sometimes causes rapid and loathsome decay.
The thread-like fibres of the spawn of the Peronospora permeate even the branches and wood of trees. Wasps are frequently seen to frequent hollow trees, probably in search of the mycelia of some of these parasitic fungi, which is identical in structure with the material of which their nests are built. Signore Panceri, professor of comparative anatomy in the university of Naples, has discovered seven species of Mucedines in the albumen of hens’ eggs.
Chemical changes in preserved animal and vegetable substances afford suitable food for the Penicillia mould, if indeed they are not the immediate cause of these changes. The threads rising from the mycelium of these moulds terminate in bundles of branchlets carrying at their summits strings of spores, like necklaces of small beads collected into bunches like tassels, white, yellowish, blue or red according to their age or kind.Figure 34represents various species of Mucedines, in whichcis the Penicillium armeniacum, andfis a spore of Helminthosporium Hoffmanni; all are magnified. Different species of the Penicillia form the blue and brick-red moulds on cheese, and the greenish and grey moulds on jam and preserved fruit. They appear as dry rot, as orange coloured spots on long kept potatoes, as mildew on cloth, silk, sugar, meat, and even on weather-beaten window glass. They can exist in metallic and poisonous solutions by decomposing the chemical combination, rejecting the metal or poison, and living on whatever nutriment may be found in the remainder. Like the larger fungi, these minute plants are sometimes poisonous; the fatal effects occasionally produced by sausages and spoilt meat are supposed to be owing to poisonous moulds.
The Mucedines conform to the law prevailing inother low organizations of having their species widely distributed. The Penicillium glaucum is found in all countries, especially in the vicinity of man; it inevitably appears in all saccharine substances, and, according to M. Fries, it is met with alike in the alps of Lapland and in the oasis of Jupiter Ammon in the Lybian desert, an example which has no parallel in the geographical distribution of the higher plants.[56]Ferment, that is to say, the yeast plant, is a peculiar condition of certain fungi, including the present species, and is capable of unlimited propagation.