Fig.72. Shoot of Horse-chestnut, of one year's growth, taken in autumn after the leaves have fallen; showing the large terminal bud and smaller axillary buds.Fig.73. Similar shoot of Shagbark Hickory, Carya alba.
Fig.72. Shoot of Horse-chestnut, of one year's growth, taken in autumn after the leaves have fallen; showing the large terminal bud and smaller axillary buds.
Fig.73. Similar shoot of Shagbark Hickory, Carya alba.
48.The Terminal Bud, in the most general sense, may be said to exist in the embryo,—as cotyledons, or the cotyledons and plumule,—and to crown each successive growth of the simple stem so long as the summit is capable of growth. The whole ascending growth of the Palm, Cycas, and the like (such as in Fig.71) is from a terminal bud. Branches, being repetitions of the main stem and growing in the same way, are also lengthened by terminal buds. Those of Horse-chestnut, Hickory, Maples, and such trees, being the resting buds of winter, are conspicuous by their protective covering of scales. These bud-scales, as will hereafter be shown, are themselves a kind of leaves.
49.Axillary Budswere formed on these annual shoots early in the summer. Occasionally they grow the same season into branches; at least, some of them are pretty sure to do so whenever the growing terminal bud at the end of the shoot is injured or destroyed. Otherwise they may lie dormant until the following spring. In many trees or shrubs these axillary buds do not show themselves until spring; but if searched for, they may be detected, though of small size, hidden under the bark. Sometimes, although earlyformed, they are concealed all summer long under the base of the leaf-stalk, which is then hollowed out into a sort of inverted cup, like a candle-extinguisher, to cover them; as in the Locust, the Yellow-wood, or more strikingly in the Button-wood or Plane-tree (Fig.74).
Fig.74. An axillary bud, concealed under the hollowed base of the leaf-stalk, in Buttonwood or Plane-tree.
Fig.74. An axillary bud, concealed under the hollowed base of the leaf-stalk, in Buttonwood or Plane-tree.
50. Theleaf-scars, so conspicuous in Fig.72, 73, under each axillary bud, mark the place where the stalk of the subtending leaf was attached until it fell in autumn.
51.Scaly Buds, which are well represented in Fig.72, 73, commonly belong to trees and shrubs of countries in which growth is suspended during winter. The scaly coverings protect the tender young parts beneath, not so much by keeping out the cold, which of course would penetrate the bud in time, as by shielding the interior from the effects of sudden changes. There are all gradations between these and
52.Naked Buds, in which these scales are inconspicuous or wanting, as in most herbs, at least above ground, and most tropical trees and shrubs. But nearly related plants of the same climate may differ widely in this respect. Rhododendrons have strong and scaly winter-buds; while in Kalmia they are naked. One species of Viburnum, the Hobble-bush, has completely naked buds, what would be a pair of scales developing into the first leaves in spring; while another (the Snowball) has conspicuous scaly buds.
53.Vigor of Vegetation from strong buds.Large and strong buds, like those of the Horse-chestnut, Hickory, and the like, contain several leaves, or pairs of leaves, ready formed, folded and packed away in small compass, just as the seed-leaves of a strong embryo are packed away in the seed: they may even contain all the blossoms of the ensuing season, plainly visible as small buds. And the stems upon which these buds rest are filled with abundant nourishment, which was deposited the summer before in thewood or in the bark. Under the surface of the soil, or on it covered with the fallen leaves of autumn, similar strong buds of our perennial herbs may be found; while beneath are thick roots, rootstocks, or tubers, charged with a great store of nourishment for their use. This explains how it is that vegetation from such buds shoots forth so vigorously in the spring of the year, and clothes the bare and lately frozen surface of the soil, as well as the naked boughs of trees, very promptly with a covering of fresh green, and often with brilliant blossoms. Everything was prepared, and even formed, beforehand: the short joints of stem in the bud have only to lengthen, and to separate the leaves from each other so that they may unfold and grow. Only a small part of the vegetation of the season comes directly from the seed, and none of the earliest vernal vegetation. This is all from buds which have lived through the winter.
54.The Arrangement of Branches, being that of axillary buds, answers to that of the leaves. Now leaves principally are eitheroppositeoralternate. Leaves areoppositewhen there are two from the same joint of stem, as in Maples (Fig.20), the two being on opposite sides of the stem; and so the axillary buds and branches are opposite, as in Fig.75. Leaves arealternatewhen there is only one from each joint of stem, as in the Oak, Lime-tree, Poplar, Button-wood (Fig.74), Morning-Glory (Fig.45,—not counting the seed-leaves, which of course are opposite, there being a pair of them); also in Indian Corn (Fig.70), and Iris (Fig.59). Consequently the axillary buds are also alternate, as in Hickory (Fig.73); and the branches they form alternate,—making a different kind of spray from the other mode, one branch shooting on one side of the stem and the next on some other. For in the alternate arrangement no leaf is on the same side of the stem as the one next above or next below it.
55. But the symmetry of branches (unlike that of the leaves) is rarely complete. This is due to several causes, and most commonly to the
56.Non-development of buds.It never happens that all the buds grow. If they did, there might be as many branches in any year as there were leaves the year before. And of those which do begin to grow, a large portion perish, sooner or later, for want of nourishment, or for want of light, or because those which first begin to grow have an advantage, which they are apt to keep, taking to themselves the nourishment of the stem, and starving the weaker buds. In the Horse-chestnut (Fig.72), Hickory (Fig.73), Magnolia, and most other trees with large scaly buds, the terminal bud is the strongest, and has the advantage in growth; and next in strength are the upper axillary buds: while the former continues the shoot of the last year, some of the latter give rise to branches, and the rest fail to grow. In the Lilac also (Fig.75), the uppermost axillary buds are stronger than the lower; but the terminal bud rarely appears at all; in its place the uppermost pair of axillary buds grow, and so each stem branches every year into two,—making a repeatedly two-forked ramification, as in Fig.76.
Fig.75. Shoot of Lilac, with winter buds; the two uppermost axillary ones strong; the terminal not developed. 76. Forking ramification of Lilac; reduced in size.
Fig.75. Shoot of Lilac, with winter buds; the two uppermost axillary ones strong; the terminal not developed. 76. Forking ramification of Lilac; reduced in size.
57.Latent Buds.Axillary buds that do not grow at the proper season, and especially those which make no appearance externally, may long remain latent, and at length upon a favorable occasion start into growth, so forming branches apparently out of place as they are out of time. The new shoots seen springing directly out of large stems may sometimes originate from such latent buds, which have preserved their life for years. But commonly these arise from
58.Adventitious Buds.These are buds which certain shrubs and trees produce anywhere on the surface of the wood, especially where it has been injured. They give rise to the slender twigs which often feather the sides of great branches of our American Elms. They sometimes form on the root, which naturally is destitute of buds; they are even found upon some leaves; and they are sure to appear on the trunks and roots of Willows, Poplars, and Chestnuts, when these are wounded or mutilated. Indeed Osier-Willows arepollarded, or cut off, from time to time, by the cultivator, for the purpose of producing a crop of slender adventitious twigs, suitable for basket-work. Such branches, being altogether irregular, of course interfere with the natural symmetry of the tree. Another cause of irregularity, in certain trees and shrubs, is the formation of what are called
Fig.77. Tartarean Honeysuckle, with three accessory buds in each axil.
59.Accessory or Supernumerary Buds.There are cases where two, three, or more buds spring from the axil of a leaf, instead of the single one which is ordinarily found there. Sometimes they are placed one over the other, as in the Aristolochia or Pipe-Vine, and in the Tartarean Honeysuckle (Fig.77); also in the Honey-Locust, and in the Walnut and Butternut (Fig.78), wherethe upper supernumerary bud is a good way out of the axil and above the others. And this is here stronger than the others, and grows into a branch which is considerably out of the axil, while the lower and smaller ones commonly do not grow at all. In other cases three buds stand side by side in the axil, as in the Hawthorn, and the Red Maple (Fig.79.) If these were all to grow into branches, they would stifle each other. But some of them are commonly flower-buds: in the Red Maple, only the middle one is a leaf-bud, and it does not grow until after those on each side of it have expanded the blossoms they contain.
Fig.78. Butternut branch, with accessory buds, the uppermost above the axil.Fig.79. Red-Maple branch, with accessory buds placed side by side. The annular lines toward the base in this and in Fig.72are scars of the bud-scales, and indicate the place of the winter-bud of the preceding year.
Fig.78. Butternut branch, with accessory buds, the uppermost above the axil.
Fig.79. Red-Maple branch, with accessory buds placed side by side. The annular lines toward the base in this and in Fig.72are scars of the bud-scales, and indicate the place of the winter-bud of the preceding year.
60.Sorts of Buds.It may be useful to enumerate the kinds of buds which have been described or mentioned. They are
Terminal, when they occupy the summit of (or terminate) a stem,
Lateral, when they are borne on the side of a stem; of which the regular kind is the
Axillary, situated in the axil of a leaf. These are
AccessoryorSupernumerary, when they are in addition to the normal solitary bud; and these areCollateral, when side by side;Superposed, when one above another;
Extra-axillary, when they appear above the axil, as some do when superposed, and as occasionally is the case when single.
Naked buds; those which have no protecting scales.
Scaly buds; those which have protecting scales, which are altered leaves or bases of leaves.
Leaf-buds, contain or give rise to leaves, and develop into a leafy shoot.
Flower-buds, contain or consist of blossoms, and no leaves.
Mixed buds, contain both leaves and blossoms.
61.Definite annual Growthfrom winter buds is marked in most of the shoots from strong buds, such as those of the Horse-chestnut and Hickory (Fig.72, 73). Such a bud generally contains, already formed in miniature, all or a great part of the leaves and joints of stem it is to produce, makes its whole growth in length in the course of a few weeks, or sometimes even in a few days, and then forms and ripens its buds for the next year's similar growth.
62.Indefinite annual Growth, on the other hand, is well marked in such trees or shrubs as the Honey-Locust, Sumac, and in sterile shoots ofthe Rose, Blackberry, and Raspberry. That is, these shoots are apt to grow all summer long, until stopped by the frosts of autumn or some other cause. Consequently they form and ripen no terminal bud protected by scales, and the upper axillary buds are produced so late in the season that they have no time to mature, nor has their wood time to solidify and ripen. Such stems therefore commonly die back from the top in winter, or at least all their upper buds are small and feeble; so the growth of the succeeding year takes place mainly from the lower axillary buds, which are more mature.
63.Deliquescent and Excurrent Growth.In the former case, and wherever axillary buds take the lead, there is, of course, no single main stem, continued year after year in a direct line, but the trunk is soon lost in the branches. Trees so formed commonly have rounded or spreading tops. Of such trees withdeliquescentstems,—that is, with the trunk dissolved, as it were, into the successively divided branches,—the common American Elm (Fig.80) is a good illustration.
Fig.80. An American Elm, with Spruce-trees, and on the left Arbor Vitæ.
Fig.80. An American Elm, with Spruce-trees, and on the left Arbor Vitæ.
64. On the other hand, the main stem of Firs and Spruces, unless destroyed by some injury, is carried on in a direct line throughout the whole growth of the tree, by the development year after year of a terminal bud: this forms a single, uninterrupted shaft,—anexcurrenttrunk, which cannot be confounded with the branches that proceed from it. Of suchspiryorspire-shapedtrees, the Firs or Spruces are characteristic and familiar examples. There are all gradations between the two modes.
65. It is a property of stems to produce roots. Stems do not spring from roots in ordinary cases, as is generally thought, but roots from stems. When perennial herbs arise from the ground, as they do at spring-time, they rise from subterranean stems.
66.The Primary Rootis a downward growth from the root-end of the caulicle, that is, of the initial stem of the embryo (Fig.5-7,81). If it goes on to grow it makes amainortap-root, as in Fig.37, etc. Some plants keep this main root throughout their whole life, and send off only small side branches; as in the Carrot and Radish: and in various trees, like the Oak, it takes the lead of the side-branches for several years, unless accidentally injured, as a strong tap-root. But commonly the main root divides off very soon, and is lost in the branches.Multiple primary rootsnow and then occur, as in the seedling of Pumpkin (Fig.27), where a cluster is formed even at the first, from the root-end of the caulicle.
Fig.81. Seedling Maple, of the natural size; the root well supplied with root hairs, here large enough to be seen by the naked eye. 82. Lower end of this root, magnified, the root seen just as root-hairs are beginning to form a little behind the tip.
Fig.81. Seedling Maple, of the natural size; the root well supplied with root hairs, here large enough to be seen by the naked eye. 82. Lower end of this root, magnified, the root seen just as root-hairs are beginning to form a little behind the tip.
67.Secondary Rootsare those which arise from other parts of the stem. Any part of the stem may produce them, but they most readily come from the nodes. As a general rule they naturally spring, or may be made to spring, from almost any young stem, when placed in favorable circumstances,—that is, when placed in the soil, or otherwise supplied with moisture and screened from the light. For the special tendency of the root is to avoid the light, seek moisture, and therefore to bury itself in the soil.Propagation by division, which is so common and so very important in cultivation, depends upon the proclivity of stems to strike root. Stems or branches which remain under ground give out roots as freely as roots themselves give off branches. Stems which creep on the ground most commonly root at the joints; so will most branches when bent to the ground, as in propagation bylayering; and propagation bycuttingsequally depends upon the tendency of the cut end of a shoot to produce roots. Thus, a piece of a plant which has stem and leaves, either developed or in the bud, may be made to produce roots, and so become an independent plant.
68.Contrast between Stem and Root.Stems are ascending axes; roots are descending axes. Stems grow by the successive development of internodes (13), one after another, each leaf-bearing at its summit (or node); so that it is of the essential nature of a stem to bear leaves. Roots bear no leaves, are not distinguishable into nodes and internodes, but grow on continuously from the lower end. They commonly branch freely, but not from any fixed points nor in definite order.
69. Although roots generally do not give rise to stems, and therefore do not propagate the plant, exceptions are not uncommon. For as stems may produce adventitious buds, so also may roots. The roots of the Sweet Potato among herbs, and of the Osage Orange among trees freely produce adventitious buds, developing into leafy shoots; and so these plants are propagated byroot-cuttings. But most growths of subterranean origin which pass for roots are forms of stems, the common Potato for example.
70. Roots of ordinary kinds and uses may be roughly classed intofibrousandfleshy.
71.Fibrous Roots, such as those of Indian Corn (Fig.70), of most annuals, and of many perennials, serve only for absorption: these are slender or thread-like. Fine roots of this kind, and the fine branches which most roots send out are calledRootlets.
72.The whole surface of a root absorbs moisture from the soil while fresh and new; and the newer roots and rootlets are, the more freely do they imbibe. Accordingly, as long as the plant grows above ground, and expands fresh foliage, from which moisture largely escapes into the air, so long it continues to extend and multiply its roots in the soil beneath, renewing and increasing the fresh surface for absorbing moisture, in proportion to the demand from above. And when growth ceases above ground, and the leaves die and fall, or no longer act, then the roots generally stop growing,and their soft and tender tips harden. From this period, therefore, until growth begins anew the next spring, is the best time for transplanting; especially for trees and shrubs.
73. The absorbing surface of young roots is much increased by the formation, near their tips, ofRoot-hairs(Fig.81, 82), which are delicate tubular outgrowths from the surface, through the delicate walls of which moisture is promptly imbibed.
Fig.83-85. Forms of tap-root.
74.Fleshy Rootsare those in which the root becomes a storehouse of nourishment. Typical roots of this kind are those of such biennials as the turnip and carrot; in which the food created in the first season's vegetation is accumulated, to be expended the next season in a vigorous growth and a rapid development of flowers, fruit, and seed. By the time the seed is matured the exhausted root dies, and with it the whole plant.
75. Fleshy roots may be single or multiple. The single root of the commoner biennials is the primary root, or tap-root, which begins to thicken in the seedling. Names are given to its shapes, such as
Conical, when it thickens most at the crown, or where it joins the stem, and tapers regularly downwards to a point, as in the Parsnip and Carrot (Fig.84);
Turnip-shapedornapiform, when greatly thickened above, but abruptly becoming slender below; as the Turnip (Fig.83); and
Spindle-shaped, orFusiform, when thickest in the middle and tapering to both ends; as the common Radish (Fig.85).
76. These examples are of primary roots. It will be seen that turnips, carrots, and the like, are not pure root throughout; for the caulicle, from the lower end of which the root grew, partakes of the thickening, perhaps also some joints of stem above: so the bud-bearing and growing top is stem.
Fig.86. Sweet-Potato plant forming thickened roots. Some in the middle are just beginning to thicken; one at the left has grown more; one at the right is still larger.Fig.87. Fascicled fusiform roots of a Dahlia:a,a, buds on base of stem.
Fig.86. Sweet-Potato plant forming thickened roots. Some in the middle are just beginning to thicken; one at the left has grown more; one at the right is still larger.
Fig.87. Fascicled fusiform roots of a Dahlia:a,a, buds on base of stem.
77. A fine example of secondary roots (67), some of which remain fibrous for absorption, while a few thicken and store up food for the next season's growth, is furnished by the Sweet Potato (Fig.86). As stated above, these are used for propagation by cuttings; for any part will produce adventitious buds and shoots. The Dahlia producesfascicled(i. e. clustered) fusiform roots of the same kind, at the base of the stem (Fig.87): but these, like most roots, do not produce adventitious buds. The buds by which Dahlias are propagated belong to the surviving base of the stem above.
78.Anomalous Roots, as they may be called, are those which subserve other uses than absorption, food-storing, and fixing the plant to the soil.
Aerial Roots, i. e. those that strike from stems in the open air, are common in moist and warm climates, as in the Mangrove which reaches the coast of Florida, the Banyan, and, less strikingly, in some herbaceous plants, such as Sugar Cane, and even in Indian Corn. Such roots reach the ground at length, or tend to do so.
Aerial Rootletsare abundantly produced by many climbing plants, such as the Ivy, Poison Ivy, Trumpet Creeper, etc., springing from the side of stems, which they fasten to trunks of trees, walls, or other supports. These are used by the plant for climbing.
Fig.88. Epiphytes of Florida and Georgia, viz., Epidendrum conopseum, a small Orchid, and Tillandsia usneoides, the so-called Long Moss or Black Moss, which is no moss, but a flowering plant, alsoT. recurvata; on a bough of Live Oak.
Fig.88. Epiphytes of Florida and Georgia, viz., Epidendrum conopseum, a small Orchid, and Tillandsia usneoides, the so-called Long Moss or Black Moss, which is no moss, but a flowering plant, alsoT. recurvata; on a bough of Live Oak.
79.Epiphytes, or Air-Plants(Fig.88), are called by the former name because commonly growingupon the trunks or limbs of other plants; by the latter because, having no connection with the soil, they must derive their sustenance from the air only. They have aerial roots, which do not reach the ground, but are used to fix the plant to the surface upon which the plant grows: they also take a part in absorbing moisture from the air.
80.Parasitic Plants, of which there are various kinds, strike their roots, or what answer to roots, into the tissue of foster plants, or form attachments with their surface, so as to prey upon their juices. Of this sort is the Mistletoe, the seed of which germinates on the bough where it falls or is left by birds; and the forming root penetrates the bark and engrafts itself into the wood, to which it becomes united as firmly as a natural branch to its parent stem; and indeed the parasite lives just as if it were a branch of the tree it grows and feeds on. A most common parasitic herb is the Dodder; which abounds in low grounds in summer, and coils its long and slender, leafless, yellowish stems—resembling tangled threads of yarn—round and round the stalks of other plants; wherever they touch piercing the bark with minute and very short rootlets in the form of suckers, which draw out the nourishing juices of the plants laid hold of. Other parasitic plants, like the Beech-drops and Pine-sap, fasten their roots under ground upon the roots of neighboring plants, and rob them of their juices.
81. Some plants are partly parasitic; while most of their roots act in the ordinary way, others make suckers at their tips which grow fast to the roots of other plants and rob them of nourishment. Some of our species of Gerardia do this (Fig.89).
Fig.89. Roots of Yellow Gerardia, some attached to and feeding on the root of a Blueberry-bush.
Fig.89. Roots of Yellow Gerardia, some attached to and feeding on the root of a Blueberry-bush.
82. There are phanerogamous plants, like Monotropa or Indian Pipe, the roots of which feed mainly on decaying vegetable matter in the soil. These areSaprophytes, and they imitate Mushrooms and other Fungi in their mode of life.
83.Duration of Roots, etc.Roots are said to be eitherannual,biennial, orperennial. As respects the first and second, these terms may be applied either to the root or to the plant.
84.Annuals, as the name denotes, live for only one year, generally foronly a part of the year. They are of course herbs; they spring from the seed, blossom, mature their fruit and seed, and then die, root and all. Annuals of our temperate climates with severe winters start from the seed in spring, and perish at or before autumn. Where the winter is a moist and growing season and the summer is dry,winter annualsprevail; their seeds germinate under autumn or winter rains, grow more or less during winter, blossom, fructify, and perish in the following spring or summer. Annuals are fibrous-rooted.
85.Biennials, of which the Turnip, Beet, and Carrot are familiar examples, grow the first season without blossoming, usually thicken their roots, laying up in them a stock of nourishment, are quiescent during the winter, but shoot vigorously, blossom, and seed the next spring or summer, mainly at the expense of the food stored up, and then die completely. Annuals and biennials flower only once; hence they have been calledMonocarpic(that is, once-fruiting) plants.
86.Perennialslive and blossom year after year. A perennial herb, in a temperate or cooler climate, usually dies down to the ground at the end of the season's growth. But subterranean portions of stem, charged with buds, survive to renew the development. Shrubs and trees are of course perennial; even the stems and branches above ground live on and grow year after year.
87. There are all gradations between annuals and biennials, and between these and perennials, as also between herbs and shrubs; and the distinction between shrubs and trees is quite arbitrary. There are perennial herbs and even shrubs of warm climates which are annuals when raised in a climate which has a winter,—being destroyed by frost. The Castor-oil plant is an example. There are perennial herbs of which only small portions survive, as off-shoots, or, in the Potato, as tubers, etc.
88.The Stemis the axis of the plant, the part which bears all the other organs. Branches are secondary stems, that is, stems growing out of stems. The stem at the very beginning produces roots, in most plants a single root from the base of the embryo-stem, or caulicle. As this root becomes adescending axis, so the stem, which grows in the opposite direction is called theascending axis. Rising out of the soil, the stem bears leaves; and leaf-bearing is the particular characteristic of the stem. But there are forms of stems that remain underground, or make a part of their growth there. These do not bear leaves, in the common sense; yet they bear rudiments of leaves, or what answers to leaves, although not in the form of foliage. The so-called stemless oracaulescentplants are those which bear no obvious stem (caulis) above ground, but only flower-stalks, and the like.
89.Stems above ground, through differences in duration, texture, and size, form herbs, shrubs, trees, etc., or in other terms are
Herbaceous, dying down to the ground every year, or after blossoming.
Suffrutescent, slightly woody below, there surviving from year to year.
SuffruticoseorFrutescent, when low stems are decidedly woody below, but herbaceous above.
FruticoseorShrubby, woody, living from year to year, and of considerable size,—not, however, more than three or four times the height of a man.
Arborescent, when tree-like in appearance or mode of growth, or approaching a tree in size.
Arboreous, when forming a proper tree-trunk.
90. As to direction taken in growing, stems may, instead of growing upright or erect, be
Diffuse, that is, loosely spreading in all directions.
Declined, when turned or bending over to one side.
Decumbent, reclining on the ground, as if too weak to stand.
AssurgentorAscending, rising obliquely upwards.
ProcumbentorProstrate, lying flat on the ground from the first.
CreepingorRepent, prostrate on or just beneath the ground, and striking root, as does the White Clover, the Partridge-berry, etc.
ClimbingorScandent, ascending by clinging to other objects for support, whether bytendrils, as do the Pea, Grape-Vine, and Passion-flower and Virginia Creeper (Fig.92,93); by their twisting leaf-stalks, as the Virgin's Bower; or by rootlets, like the Ivy, Poison Ivy, and Trumpet Creeper.
TwiningorVoluble, when coiling spirally around other stems or supports; like the Morning-Glory (Fig.90) and the Hop.
Fig.90. Twining or voluble stem of Morning-Glory.
91. Certain kinds of stems or branches, appropriated to special uses, have received distinct substantive names; such as the following:
92.A Culm, or straw-stem, such as that of Grasses and Sedges.
93.A Caudexis the old name for such a peculiar trunk as a Palm-stem; it is also used for an upright and thick rootstock.
94.A Suckeris a branch rising from stems under ground. Such are produced abundantly by the Rose, Raspberry, and other plants said to multiply "by the root." If we uncover them, we see at once the great difference between these subterranean branches and real roots. They are only creeping branches under ground. Remarking how the upright shoots from these branches become separateplants, simply by the dying off of the connecting under-ground stems, the gardener expedites the result by cutting them through with his spade. That is, he propagates the plant "by division."
95.A Stolonis a branch from above ground, which reclines or becomes prostrate and strikes root (usually from the nodes) wherever it rests on the soil. Thence it may send up a vigorous shoot, which has roots of its own, and becomes an independent plant when the connecting part dies, as it does after a while. The Currant and the Gooseberry naturally multiply in this way, as well as by suckers (which are the same thing, only the connecting part is concealed under ground). Stolons must have suggested the operation oflayeringby bending down and covering with soil branches which do not naturally make stolons; and after they have taken root, as they almost always will, the gardener cuts through the connecting stem, and so converts a rooting branch into a separate plant.
96.An Offsetis a short stolon, or sucker, with a crown of leaves at the end, as in the Houseleek (Fig.91), which propagates abundantly in this way.
Fig.91. Houseleek (Sempervivum), with offsets.
97.A Runner, of which the Strawberry presents the most familiar and characteristic example, is a long and slender, tendril-like stolon, or branch from next the ground, destitute of conspicuous leaves. Each runner of the Strawberry, after having grown to its full length, strikes root from the tip, which fixes it to the ground, then forms a bud there, which develops into a tuft of leaves, and so gives rise to a new plant, which sends out new runners to act in the same way. In this manner a single Strawberry plant will spread over a large space, or produce a great number of plants, in the course of the summer, all connected at first by the slender runners; but these die in the following winter, if not before, and leave the plants as so many separate individuals.
98.Tendrilsare branches of a very slender sort, like runners, not destined like them for propagation, and therefore always destitute of buds or leaves, being intended only for climbing. Simple tendrils are such as those of Passion-flowers (Fig.92). Compound or branching tendrils are borne by the Cucumber and Pumpkin, by the Grape-Vine, Virginia Creeper, etc.
Fig.92. A small Passion-flower (Passiflora sicyoides), showing the tendrils.
Fig.92. A small Passion-flower (Passiflora sicyoides), showing the tendrils.
99. A tendril commonly grows straight and outstretched until it reaches some neighboring support, such as a stem, when its apex hooks around it to secure a hold; then the whole tendril shortens itself by coiling up spirally, and so draws the shoot of the growing plant nearer to the supporting object. But the tendrils of the Virginia Creeper (Ampelopsis, Fig.93), as also the shorter ones of the Japanese species, effect the object differently, namely, by expanding the tips of the tendrils into a flat disk, with an adhesive face. This is applied to the supporting object, and it adheres firmly; then a shortening of the tendril and its branches by coiling brings up the growing shoot close to the support. This is an adaptation for climbing mural rocks or walls, or the trunks of trees, to which ordinary tendrils are unable to cling. The Ivy and Poison Ivy attain the same result by means of aerial rootlets (78).
Fig.93. Piece of the stem of Virginia Creeper, bearing a leaf and a tendril. 94. Tips of a tendril, about the natural size, showing the disks by which they hold fast to walls, etc.
Fig.93. Piece of the stem of Virginia Creeper, bearing a leaf and a tendril. 94. Tips of a tendril, about the natural size, showing the disks by which they hold fast to walls, etc.
100. Some tendrils are leaves or parts of leaves, as those of the Pea (Fig.35). The nature of the tendril is known by its position. A tendril from the axil of a leaf, like that of Passion-flowers (Fig.92) is of course a stem, i. e. a branch. So is one which terminates a stem, as in the Grape-Vine.
101.SpinesorThorns(Fig.95, 96) are commonly stunted and hardened branches or tips of stems or branches, as are those of Hawthorn, Honey-Locust, etc. In the Pear and Sloe all gradations occur between spines and spine-like (spinescent) branches. Spines may be reduced and indurated leaves; as in the Barberry, where their nature is revealed by their situation, underneath an axillary bud. Butprickles, such as those of Blackberry and Roses, are only excrescences of the bark, and not branches.
Fig.95. A branching thorn of Honey-Locust, being an indurated leafless branch developed from an accessory bud far above the axil: at the cut portion below, three other buds (a) are concealed under the petiole.Fig.96. Spine of Cockspur Thorn, developed from an axillary bud, as the leaf-scar below witnesses: an accessory leaf-bud is seen at its base.
Fig.95. A branching thorn of Honey-Locust, being an indurated leafless branch developed from an accessory bud far above the axil: at the cut portion below, three other buds (a) are concealed under the petiole.
Fig.96. Spine of Cockspur Thorn, developed from an axillary bud, as the leaf-scar below witnesses: an accessory leaf-bud is seen at its base.
102. Equally strange forms of stems are characteristic of the Cactus family (Fig.111). These may be better understood by comparison with
103.Subterranean Stems and Branches.These are very numerous and various; but they are commonly overlooked, or else are confounded with roots. From their situation they are out of ordinary sight; but they will well repay examination. For the vegetation that is carried on under ground is hardly less varied or important than that above ground. All their forms may be referred to four principal kinds: namely, theRhizoma(Rhizome) orRootstock, theTuber, theCormor solid bulb, and the trueBulb.
Fig.97. Rootstocks, or creeping subterranean branches, of the Peppermint.
Fig.97. Rootstocks, or creeping subterranean branches, of the Peppermint.
104.The Rootstock, or Rhizoma, in its simplest form, is merely a creeping stem or branch growing beneath the surface of the soil, or partly covered by it. Of this kind are the so-calledcreeping,running, orscaly roots, such as those by which the Mint (Fig.97), the Couch-grass, or Quick-grass, and many other plants, spread so rapidly and widely,—"by the root," as it is said. That these are reallystems, and not roots, is evident from the way in whichthey grow; from their consisting of a succession of joints; and from the leaves which they bear on eachnode, in the form of small scales, just like the lowest ones on the upright stem next the ground. They also produce buds in the axils of these scales, showing the scales to be leaves; whereas real roots bear neither leaves nor axillary buds. Placed as they are in the damp and dark soil, such stems naturally produce roots, just as the creeping stem does where it lies on the surface of the ground.
105. It is easy to see why plants with these running rootstocks take such rapid and wide possession of the soil, and why they are so hard to get rid of. They are always perennials; the subterranean shoots live over the first winter, if not longer, and are provided with vigorous buds at every joint. Some of these buds grow in spring into upright stems, bearing foliage, to elaborate nourishment, and at length produce blossoms for reproduction by seed; while many others, fed by nourishment supplied from above, form a new generation of subterranean shoots; and this is repeated over and over in the course of the season or in succeeding years. Meanwhile, as the subterranean shoots increase in number, the older ones, connecting the successive growths, die off year by year, liberating the already rooted side-branches as so many separate plants; and so on indefinitely. Cutting these running rootstocks into pieces, therefore, by the hoe or the plough, far from destroying the plant, only accelerates the propagation; it converts one many-branched plant into a great number of separate individuals. Cutting into pieces only multiplies the pest; for each piece (Fig.98) is already a plantlet, with its roots and with a bud in the axil of its scale-like leaf (either latent or apparent), and with prepared nourishment enough to develop this bud into a leafy stem; and so a single plant is all the more speedily converted into a multitude. Whereas, when the subterranean parts are only roots, cutting away the stem completely destroys the plant, except in the rather rare cases where the root freely produces adventitious buds.