226. In solid form the stem is extremely variable; the following common terms relating to it :

102 are

Terete; half-terete; compressed; plano-compressed ; two-edged d; acuteangled; obtuse-angled ; triangular; quadrangular; quinquangulari; octangular; multangular; triquetrous; tetraquetrous; obscurely triquetrous m ; trilateral"; quadrilateral; quinquelateral r. The figures show that

Fig. 104.-a Old corm; b present corm; c coming corm, in a Crocus.

Fig. 103.-Colchiam; r Roots; fleaf; a old stem of the previous year withered; a' present corm; a" beginning of new corm.

OF THE LEAF-BUDS.

39

VII. OF THE LEAF-BUDS.

LEAF-BUDS

227. BUDS are of two kinds, Leaf-buds and Flower-buds. (Bourgeon, Fr.) consist of rudimentary leaves surrounding a growing (vital) point, which lengthens upwards, and produces leaf after leaf upon

its surface.

The accuracy of this statement is conclusively established by the excellent observations of De Mercklin, who has proved that the growing point is not an imaginary organ, but a cellular tumour having a peculiar organization. 228. FLOWER-BUDS (Bouton, Fr.) consist of rudimentary leaves surrounding a fixed (vital) point, and assuming, when fully developed, the form of floral envelopes or apparatus.

229. Notwithstanding this difference, a leaf-bud sometimes indicates a tendency to become a flower-bud; and flower-buds frequently assume the character of leaf-buds; Ex. Monstrous Pears.

This will be more particularly adverted to in speaking of the Flower.
230. In appearance, a leaf-bud 10
[106 is a collection of scales ar-
ranged symmetrically one above the other. These scales are
rudimentary leaves. The centre over which they are placed, or
the growing point, is cellular substance coated with a thin stratum
of spiral vessels; and these two parts answer to the pith and the
medullary sheath in Exogens.

De Mercklin has shown that the evolution of a leaf-bud is not very
unlike the gradual drawing out of the slides of a telescope; that
young leaves are continually formed below the end of the growing
point, and that, consequently, the lowest leaves of a leaf-bud are
necessarily the oldest. That the scales are rudimentary leaves was
long ago shown by the gradual changes which take place in the scales
when a bud unfolds 107; the careful observer just alluded to has
demonstrated that leaves are always, when very young, shaped like the scales
of the bud; in fact, the latter are leaves formed at the latter end of the year,
and arrested in their growth.

106

231. By the growth of a leaf-bud a branch is formed; such of the scales as are alive gradually changing into true leaves as vegetation advances 107 c. 232. Sometimes leaf-buds separate spontaneously from the stem (are deciduous), and are then called bulbills or bulblets 107f; Ex. Lilium bulbi

ferum.

233. In other cases they are of large size, and are formed underground; they then form bulbs, or scaly bulbs 107 a b

234. In bulbs, other young buds or bulbs, called cloves, are often formed in the axils of the scales, as in Garlic; and these gradually destroy the old bulb by feeding upon it.

In like manner corms produce other corms, and are destroyed by their offspring, as has been already shown (217). Thus, in some Gladioles 107 de, an old corm produces the new one always at its point; the latter is then seated on the remains of its parent, and, being in like manner devoured by its own offspring,

107

becomes the base of the third generation 103 e This process enables such plants by degrees to raise themselves out of the earth in which they were born.

235. Both corms and bulbs are reservoirs of nutriment in either a starchy or mucilaginous condition, or both.

236. Leaf-buds are of two kinds, the regular and the adventitious. 237. Regular or normal Leaf-buds are only found in the axils of leaves. Commonly they are single, but in some plants they exist in great numbers, and then they obey two different laws of development; the lowermost in some being

the most advanced, as in Lonicera tatarica 109; and the highest in others, as in the Walnut 108. Several are sometimes on the same plane, as in the Willow or Poplar, and then the laterals have been supposed to belong to stipules.

238. They exist in a developed or undeveloped state in the axils of all leaves, and of all modifications of leaves.

239. Therefore they may be expected to appear at the axils of scales of the bud, of stipules, of bracts, of sepals, of petals, of stamens, and of carpels, in all which situations they are generally undeveloped; for these different organs are all modifications of leaves.

The proofs of this theory will be given hereafter.

240. They are frequently not called into action, even in the axils of leaves, but lie dormant.

241. As regular buds are only found in the axils of leaves, or of their modifications, and as branches are always the development of buds, it

ADVENTITIOUS LEAF-BUDS.

41

follows, that, whatever may be the arrangement of the leaves, the same will be the disposition of the branches; and vice versa.

242. This corresponding symmetry is, however, continually destroyed by the unequal development of buds, or by the accidental destruction of a part

of them.

243. Leaf-buds which are formed among the tissue of plants subsequently to the development of the stem and leaves, and without reference to the latter, are called latent, adventitious, or abnormal.

244. Adventitious Leaf-buds may be produced from any part of the medullary system, or wherever cellular tissue is present. It has been distinctly proved, that, while roots are prolongations of the vertical or woody system, leaf-buds universally originate in the horizontal or cellular system. 245. They are formed in the root, among the wood, and at the margin or on the surface of leaves, whether perfect or rudimentary.

This is now a well-known fact. The following example of it was related in the Gardeners' Chronicle for October 18th, 1845:-" A Hyacinth bulb, in a state of rapid putrefaction, while kept in contact with the cold water of a hyacinth-glass in a dwelling-house, entirely renewed its vitality when removed to a warm situation. The decay had eaten completely through the base of the scales into the very heart of the hyacinth, which was putrid. The foul slimy matter was wiped off, and the bulb was placed, its base upwards, on a layer of warm sand, covering the bottom of an earthen pan. The sand was moistened with water of a temperature of 80°, or thereabouts; a bell-glass was placed over the bulb, with its edges pressed into the sand and the apparatus was put on a shelf near a

north window, about four feet above an Arnott stove in constant action. From time to time warm water was given by pouring it upon the sand between the edge of the earthen pan and the side of the bell-glass. Decay was immediately arrested; for some time the bulb remained dormant; but, by degrees, healthy granulations made their appearance, displacing the decayed matter; and in a few weeks a fine crop of young bulbs sprouted forth on the surface of the scales and on the edges of the healed-up sores." In this case, as in all of a similar nature, the new buds appeared from the parenchyma exclusively; and many of them became completely organized as small bulbs before the vitality of the parent

bulb was exhausted. The bulbs formed on the petiole of Arum ternatum 103 c are of a similar origin.

246. They are constructed anatomically exactly as regular buds, having a growing point in their centre.

247. Embryo-buds are woody nodules found in the bark of trees, and appear to be rudimentary branches formed without leaves, within a space in which they are forcibly pressed upon by surrounding tissue.

.

They are common in the bark of the Beech, the Elm, and the Cedar of Lebanon ; and not uncommonly grow into stunted branches. Very curious examples of such growth occasionally occur in damp tropical countries.

247 a. The manner in which the leaves are folded in the leaf-bud varies with species, and is called the vernation of a plant. The following are the principal forms:

Fig. 111.--a a Convolute; b involute; e plicate; d revolute; e obvolute; fequitant.