Fig. 34. Mucedines:—a, Aspergillus glaucus;b, Aspergillus dubius;c, Penicillium armeniacum;d, Sepedonium mycophilum;e, Helminthosporium nodosum;f, Helminthosporium Hoffmanni, spore;g, Zygodesmus fuscus.
Fig. 34. Mucedines:—a, Aspergillus glaucus;b, Aspergillus dubius;c, Penicillium armeniacum;d, Sepedonium mycophilum;e, Helminthosporium nodosum;f, Helminthosporium Hoffmanni, spore;g, Zygodesmus fuscus.
Fig. 34. Mucedines:—a, Aspergillus glaucus;b, Aspergillus dubius;c, Penicillium armeniacum;d, Sepedonium mycophilum;e, Helminthosporium nodosum;f, Helminthosporium Hoffmanni, spore;g, Zygodesmus fuscus.
The real spore-bearing filaments of the Penicillium glaucum are only developed in air, for when the spores of that fungus are kept submerged in a liquid favourable for their growth, as in a saccharine solution, or the juice of the grape, they form an aquatic mycelium on the filaments of which cells are produced, and carbonic acid gas is given out. These cells increase by budding or division into chains of ferment, easily separated into single cells. The Penicillium glaucum is thus developedin all kinds of liquids, and in almost all kinds of conditions; even the peculiar knotty filaments observed in its submerged mycelium are not constant in different liquids. M. Hoffmann has observed with certainty the passage of Penicillium glaucum into Penicillium candidum, into a sulphur-coloured Penicillium, and, lastly, into the Coremium glaucum, so that this fungus is polymorphous, although the conditions under which the changes take place are unknown.[57]
It appears that substances and liquids do not ferment spontaneously, for upon examining with a microscope the dust obtained by scraping the exterior of gooseberries, plums, vine leaves, potatoes, &c., M. Hoffmann found the short chains of the Torula, the necklace-like ferments of the Mucedines, and the chaplets of others. Some had already begun to germinate, and were developed readily when put into water. They had no doubt been carried by the wind from the dry refuse of fermented substances which are thrown away.
Fig. 35. Torula Cerevisiæ, showing successive stages of cell multiplication.
Fig. 35. Torula Cerevisiæ, showing successive stages of cell multiplication.
Fig. 35. Torula Cerevisiæ, showing successive stages of cell multiplication.
The yeast of beer was at one time considered to consist entirely of the cells and chains of the Torula Cerevisiæ (fig. 35). This, which is one of the Coniomycetes of the order Torulacei, is in its early stage a colourless transparent globe capable of endless increase by budding. When in a liquid favourable to its growth, as the wort of malt, buds in the form of young cells spring from the walls of the globes; these soon become perfect and acquire buds also, so that in a few hours the parent cellsdevelop themselves into rows of four or five globes, which remain in contact while the plant is growing, but separate if anything checks the fermentation. The full development of the plant only takes place when the fermentation is allowed to continue for some time, and then it is capable of producing a variety of forms, which show that it has other modes of reproduction besides budding.[58]In fact, when the fermentation is active in the upper parts of the liquid it appears in chaplets of from four to twelve articulations, or sometimes it ramifies into little branches.
More recent observations show that yeast is a peculiar state of the mycelium of various fungi, of which, as already stated, a large proportion is believed to consist of Penicillium glaucum, though it is known that other kinds of mould also enter into its composition. These plants grow naturally in a state of exposure to the atmosphere, but they have the property of also developing themselves when submerged; and as in this unnatural condition, which they bear when developed as yeast, they cannot produce their proper fruit, they propagate themselves by means of shoots from the altered mycelium. It has been observed that mechanical injury destroys the vitality of German yeast, which consists of yeast globules in a dried state. Thus a fall on the ground, or a bruise caused by a blow or by careless handling, will kill the plant, and such dead yeast becomes dark-coloured and glutinous, and soon acquires an offensive smell.
The form of Penicillium glaucum which produces acetic fermentation, known as the vinegar plant, has a filamental submerged instead of a vesicular mycelium.
Ferments may be formed in the wort of beer, in the solutions of grape and cane sugar, in the juice of gooseberries, currants, &c., by means of the submerged sporesof the Uredines segetum and Rosæ, of Ascophora elegans, Mucor Mucedo, Periconia hyalina and others. There are active exchanges continually going on between the contents of the globules of ferments and the exterior liquid, and therefore a continual chemical action.[59]
M. Pasteur’s experiments on the nourishment of the Mucedines concur with the observations of others in showing that these plants are the origin of all fermentation properly so called. When he put a mere trace of the beer yeast fungus into pure water holding in solution the three crystallizable substances, sugar candy, an ammoniacal salt, and some phosphates, the globules of yeast were seen to multiply, deriving their nitrogen from the ammoniacal salt, their carbon from the sugar, and their mineral material from the phosphates; at the same time the sugar fermented. The same results were obtained from lactic yeast. M. Pasteur now sowed the spores of the Penicillium, or of some other mucedinous fungus in pure distilled water holding in solution the same ingredients, except that an acid salt of ammonia was employed to prevent the development of infusoria, which would soon have stopped the progress of the microscopic plant by absorbing the oxygen without which fungi cannot live. The result was the same as in the preceding case. There is consequently a complete analogy between the ferments, the mucedines, and plants of more complex structure. If in these experiments any one of the principles in the solution be omitted, the vegetation is arrested. The quantities of these substances in the air, the water, or in the spores themselves, are not sufficient to make up for the suppression of any one of them. For example, the carbonic acid in the air or water does not make up for the omission of the sugar. The mucedines and fungi generally obtain their carbon from their food and from rain water, forrain water holds in solution nitrates and ammoniacal salts together with salts of potash and lime, and M. Barral has ascertained the existence of phosphates also. M. Barral found that the nitrates and ammonia disappear under the influence of cryptogamic plants.[60]
In the genus Oidium, belonging to the Mucedines, the short threads have a string of spores, like a necklace of beads, on their tops. Species of this genus are found on damp paper and honeycombs; also on decayed oranges, and other spoilt fruits.
The family of theAscomycetesproduces spore-bearing cells, called sporidia, enclosed in long cylindrical sacs or asci, in the definite numbers two, four, eight, sixteen, thirty-two, &c. The great characteristic of this large group, consisting of six orders, is the fleshy soft texture and the more or less complete exposure of the fructiferous surface. In one division the asci are persistent; this includes the Elvellacei, the Tuberacei, the Phacidiacei, and the Sphæriacei. In the other division the asci are often evanescent, and this includes the Perisporiacei and the Onygenei.
The genera Peziza and Helvella are the principal fungi belonging to the order Elvellacei. The Pezizæ are a very numerous race, and consist of brilliantly coloured little cups, with or without stems, and more or less concave. They grow in the cooler part of the temperate zone, many show themselves in spring, and some of the largest and most beautiful appear during the melting of the snow.[61]A few are subterranean, and 128 species inhabit Great Britain, many growing on the ground, others on stumps of trees, dead sticks and timber, on living plants, damp walls, &c. They are singularly beautiful, including ‘many of the most elegantfungi, from the little white and red Peziza elegans, which is sprinkled over almost every fallen twig of the larch and other conifers; the pale toothed cups of the P. coronata, which abounds on the dead stems of herbaceous plants; the scarlet P. scutellata with its edge fringed with tawny hairs, and the graceful mouse-grey P. macropus, to the gorgeous P. coccinea, which attracts attention from its elegant form and bright colours; the more irregular, but not less brilliant P. aurantia, and the font-shaped P. acetabulum, which might form an elegant pattern for an architect or silversmith. Fifty others might be mentioned of equal pretensions to grace of form and brilliancy of colouring.’[62]Some of the genus are peculiar in their fructification, for in several plants of this group, besides asci containing eight sporidia, M. Tulasne met with cells full of eel-shaped particles like those in the Algæ, and although without motion he considered them to be analogous to the pollen of flowering plants. In the Peziza aurantia, however, the particles were staff-shaped and motile.
The genus Helvella may be regarded as Peziza with the cup inverted; consequently, it assumes the character of a pileus or hat, like a common mushroom, though often very different in shape, and, instead of spore-bearing gills, it has asci containing eight sporidia sunk in its fleshy texture. The pileus is ovate or mitre-shaped in some species and the margin free, in others it is more or less attached to the stem. When the pileus and stem are perfectly soldered together, we get the club-shaped species of the group.
Some obscure forms of this group, forming the genus Ascomycetes, cause the leaves of the peach, walnut, and pear to blister. They consist of little more than asci, accompanied by short necklace-shaped thread.
The Morchella esculenta, which is the morel, is soplentiful in some parts of England, that it is used for making katsup; while the Cyttaria, which is indigenous in the southern hemisphere, is the staple food of the Fuegians during many months of the year; its subgelatinous consistence indicates a nutritious principle. This species has the peculiarity of growing upon living branches, after the manner of the jelly-like fungus of the juniper.
M. Tulasne has discovered in Peziza, and in the genus Bulgaria and others, certain minute bodies, which he considered to be of the nature of the eel-shaped particles or antherozoids in the Algæ. Besides, he has shown that several species of Peziza have a second form of fruit. Fries had long before pointed out the identity of Fusarium tremelloides and the orange coloured Peziza common on nettle stems. Many of the larger Pezizæ and Helvellæ eject their sporidia with great elastic force. This is particularly remarkable in the Peziza vesiculosa, common in hot-beds, when the sun is shining; the least agitation raises a visible cloud of sporidia like vapour. The motions of the sporidia in the genus Vibrissea, which grows on twigs partly immersed in water, is very peculiar. They are exceedingly long and slender, and, when partly ejected, they wave about in the sunshine till they are expelled.
The fungi of the order Tuberacei are nearly all subterranean, and their fruit-bearing surface, as in the truffle, is internal. The asci are either irregularly deposited in cavities, or in the denser tubers they are sprinkled through a dark substance which is mottled with a paler tissue. The truffle, which is the most important and best known of the order, has a dark corrugated exterior, and the asci are represented by large pyriform sacs containing sporidia covered with a reticulated or spinose coat; but these spines are only the angles of continuous cells, and are beautiful microscopicobjects. Truffles prefer calcareous soil, and a temperate climate. In England, they are found in Rutlandshire, and numerous species grow in Northamptonshire, but they are smaller than the continental truffles, which increase in abundance and size towards the south, and have their maximum in Italy, where they grow on the roots of trees and vines, and are hunted by dogs, or traced by the presence of a peculiar fly, and dug up for sale. Sometimes the dogs dig them up, to the annoyance of the proprietors of vineyards, from the mischief they do to the roots of the vines.
The Sphæriacei, another order of Ascomycetes, are enormously numerous. There are 1,000 well known species of this order, and probably twice as many undetermined; for there is scarcely a twig or dry branch in the forests, hedges, or gardens on which they may not be found. The rose tree, the oak, and other plants harbour more than one species at a time. The genus Cordyceps and many so-called species of Sphæria are only the ultimate development of fungi of other families. The Cordyceps purpurea, discovered by M. Tulasne on the ergot of wheat, has a short, upright, slender stem, with a minute pale purple globose fruit-bearing head. In this ergotized state the white substance of the grain is converted into a firm mass without any appearance of meal, and having very powerful properties. When sown, it is found to produce the Cordyceps. Mr. Currey found the same plant on the ergot of the common reed, and there are several other species of Cordyceps, all of which are only the second form of ergot. To these may be added the Cordyceps militaris of Ehrenberg, already shown (p.283) to be the ultimate development of the Isaria, which attacks the caterpillars of the bramble moth; and the Cordyceps Robertsii, which grows like a bunch of rushes from the head of the Hepialus virescens of New Zealand; whilst a kind of wasp in theWest Indies, which continues to fly about after it is attacked, is at last killed by branching Cordyceps, which project from its head like a pair of antlers. But the largest of all these parasites grows on an enormous larva found on the banks of the river Murrumbidgee in Australia. It appears that species of Sphæriæ are parasitic on insects of very different affinities in China, America, and Europe. It may be presumed that, like the Cordyceps militaris, they are the ultimate development of fungi belonging to other families.
Fig. 36. Sphæriacei:—Sphæria Desmazierii;a, ascus;b, sporidia;c, mycelium with conidia. Mucedines:—d, Botrytis curta.
Fig. 36. Sphæriacei:—Sphæria Desmazierii;a, ascus;b, sporidia;c, mycelium with conidia. Mucedines:—d, Botrytis curta.
Fig. 36. Sphæriacei:—Sphæria Desmazierii;a, ascus;b, sporidia;c, mycelium with conidia. Mucedines:—d, Botrytis curta.
In the genus Sphæria the fungus springs at once from its mycelium, and consists of a perithecium or external case, to the internal walls of which the asci are fixed. Each ascus contains eight sporidia or spore cells, and when the fruit is ripe the asci are emitted through a pore or slit in the perithecium or external coat.Fig. 36represents the fructification of Sphæria Desmazierii.Sphæria bombarda is like an assemblage of minute black beads lying flat and crowded together upon decayed wood; each bead is an oblong vesicle pierced at the apex for the emission of the microscopic sporidia, or spore cells. The Sphæria aquila, found upon decayed wood, has its fruit-bearing vessels seated upon thickly matted fine threads. In some species they are in tufts; others have bottle-shaped perithecia sunk into the stems of the berberry, laburnum, and decayed oak palings; and lastly the candle snuff Sphæria may frequently be seen like patches of soot at the bottom of stakes or gate posts. More than two hundred well ascertained species of the genus Sphæria are native in Great Britain alone.
The genus Nectria, which forms a connecting link between the genera Peziza and Sphæria, has several interesting species, as the Nectria Peziza, which grows in a congeries of most minute cups forming a bright orange-coloured patch on decayed stumps of trees.
In the order Perisporacei the perithecia, or external cases, are free and become dehiscent at last, but when young these fungi consist of cellular jointed filaments like necklaces, rising upright from their mycelia, and bearing reproductive bodies. In this state they constitute the mildew on the vine, rose tree, turnip, hop, pea, &c. They are true parasites, appropriating the juices, and filling up the breathing pores of the leaves, so as to cause disease and often death. The vine mildew, which has been called Oïdium Tuckeri, but which is now supposed to be an imperfect state of Erysiphe, never advances beyond this state, consequently it never has more than one form of fruit. Mr. Berkeley has discovered that, on the contrary, the hop and pea mildews, which belong to the genus Erysiphe, have five different modes of reproduction. The destructive power of these fungi is strongly illustrated by the extraordinaryenergy of their mycelia in draining the vital juices of the plants on which they live in order to form such various kinds of fruit; and the quantity of fruit produced is so enormous, that if the whole were to germinate no genus of plants for which they have an affinity could escape annihilation. Other species of Erysiphe have at least three different modes of reproduction. The perithecia of some of these fungi are beautiful objects for the microscope.
The Physomycetes, which form the sixth and last order of the great fungus family, have bladder-like fertile cells scattered on threads, the number of sporidia within the cells being indefinite. The Antennariei are dark coloured felt-like fungi which run over the leaves of living trees, and have fruit on black threads, which in some species, when magnified, resemble the antennæ of certain beetles. The species of this order are not common in Britain, and they are supposed to be only a condition of some other fungi. They are certainly spore-bearing plants, yet the fruit-bearing cells of the Antennaria Robinsonii sometimes contain a ready formed miniature of the parent plant waiting to be set free,—a singular analogy between these microscopic fungi and flowering plants.
The order Mucorini, or moulds, has threads springing from the spawn, bearing on their extremities large vascular sacs containing asci with spore cells. The genus Ascophora contains several remarkable species, as Ascophora elegans, which has two kinds of fruit, and attacks bread while yet hot from the oven: however, the spores were probably in the dough, for it has been ascertained that the spores of some of the lower fungi retain their vitality after being exposed to the temperature of boiling water. The Mucors are probably found on decayed and decaying matter all over theworld; they grow on fat, on greasy walls, and on decaying fruit and vegetables.
The extreme minuteness of the reproductive bodies of the microscopic fungi, many of which are not more than the 20,000th part of an inch in diameter, and their extraordinary and varied forms even in the same plant, have made these fungi one of the most difficult studies in the whole science of botany. There is still some obscurity with regard to those minute motile bodies supposed to be male particles, and their analogues, which have not been seen, or have rarely been seen to germinate. These bodies have been observed in comparatively few genera, and nothing more than mere molecular motion has been observed in them.
One of the most unaccountable circumstances in the history of the lower fungi is their sudden appearance in immense numbers, and the rapid extension of disastrous and destructive epidemics caused by them among plants and animals, as the potato murrain and the vine disease, which, though widely spread through Europe and Madeira, leaves the North American vines unscathed, whether grown at home or abroad. The black mildews at one time raged so much in the Azores and Ceylon as to threaten the complete annihilation of the orange and coffee plantations. Their ravages have been scarcely less among the olive trees in some parts of Europe; and the Lanosa nivalis, which grows in the melting snow in spring, is supposed to be the cause in many instances of the death of the germs of the sprouting rye. The destructive course of most of these has abated, but the silkworm disease still continues. The fungi require warmth and a moderate degree of moisture for their development, but the unwonted multitudes in which the parasites occasionally appear, possibly indicate some meteoric influences of which we are ignorant.