leaf is due to the form and arrangement of the bud.

M. Emery1 has made some criticisms on my suggestions, which, however, I need not notice, for, having merely seen a short and incorrect abstract, and not having taken the trouble to refer to the original paper, he misunderstood my view, as M. Devaux pointed out at the

FIG. 18.-ARRANGEMENT OF YOUNG LEAVES OF LIRIODENDRON. A corresponds with leaf No. 6 in C; B, next younger leaf; C, ground plan of a bud, showing successive leaves (1-7), with stipules (St 5, &c.)

time. I should gather also from his remarks that he can never have examined a bud in a very early state.

Or take, again, the case of the Oak and Beech. Both have a conical bud, and the young leaves are protected by stipules. I shall presently refer to them again from this point of view. For the moment I am dealing

1 Bull. Soc. Bot. France, 1888, p. 327.

with the form of the leaf only. In both species the leaves, like those of Liriodendron, are conduplicate.

The leaves are in both species of about equal length, or those of the Oak are the longer; but the buds of the

Beech (fig. 19) are much longer than those of the Oak (fig. 20). The young leaves of the Beech are able to lie straight in the bud; those of the Oak have not room to do so, and are, consequently, bent somewhat like a bow along the midrib. Now, if the outer edge

were straight, the result would be that when the young leaf emerged and straightened itself the edge must tear. This, however, is avoided by its being thrown into folds; and this, I believe, accounts for the lobes and bays so characteristic of the Oak leaf.

DORMANT AND ADVENTIVE BUDS

As a rule each leaf has a single bud in its axil; but there are two other classes of buds about which I must say a few words. In some species not merely one, but several buds arise in the axil. They appear to have been In such cases as, for in

first noticed by Tristan (3). stance, the Robinia ('Acacia') all but one of these, after attaining a certain stage of growth, become quiescent, and are gradually covered over by the bark. Such buds are known as 'dormant.' They may remain in the same state for years, but if the growing shoots are injured in the struggle for existence these reserves are called into the field. Their presence is often connected with that of thorns, as in Robinia, Gleditschia, Colletia, Genista, &c.; or with tendrils, as in Passiflora.

Another class of buds has been termed by Du Petit Thouars' adventive' buds. They appear, especially in certain plants, on the leaves, internodes, and roots. They may be divided into two classes-natural and accidental.

Natural adventive buds are formed by Cardamine pratensis, Dentaria bulbifera, Bryophyllum calycinum,

C

a considerable number of Dicotyledonous and Monocotyledonous plants, and many ferns.

A common example occurs in any abandoned field or waste ground bordered by Elm trees. The young plants which shoot up everywhere are not seedlings, but are formed by adventitious buds on the roots of the old trees; the considerable distance at which they appear from the parent emphasises the great length of the roots. Similarly, when a tree is cut down the ground becomes covered with a thick growth of young shoots, springing up rapidly, at the expense of the nourishment stored up in the roots which remain in the ground. Such shoots are also common in Poplars, Limes, many fruit trees, &c.

Accidental adventive buds are those which appear if the plant is maimed or wounded; or if a leaf, say of Begonia, is detached from the parent plant and placed on damp earth.

Goebel, in his recently published ‘Organographie,' figures an interesting case of the growth of a new plant at the end of the stalk of a detached leaf. The plant in question is a garden hybrid belonging to the same family as Gloxinia (fig. 21). The leaf was taken from a plant which was just about to flower, and the adventitious shoot has straightway produced flowers.

To eradicate Docks from a garden the whole plant must be removed, as adventitious buds will arise on any broken piece of root which is left behind The same

applies to Dandelions or Plantains.

The natural

adventive buds appear on definite parts of the plant, according to the species; in accidental adventive buds the place of origin depends on that of the injury.

FIG. 21.-ACHIMENES HAAGEANA, showing development of a new flowering plant consisting of root and flowering-shoot.

Adventitive shoots may arise, like normal shoots, exogenously; but endogenous development generally occurs when they arise from older parts of stems or roots. In some cases they are formed by the direct conversion of the growing-point of a root, as in Bird's Nest Orchid (Neottia Nidus-Avis), Catasetum tridentatum, &c.