Page:The Botany of the Antarctic Voyage.djvu/335

Falklands, etc.] The woody plates of the various branches of the Myzodendron all meet in its expanded base, and are there strangely convoluted and contorted, enclosing masses of brown and dead cellular tissue, probably consisting in part of the alburnum of the beech deposited there, as well as of the decayed medullary rays of the Myzodendron. Lower down, the woody plates, much, reduced in size, slightly converge and meet the layers of wood of the beech; these may perhaps come into actual contact, but generally, if not always, there is a deposit of disintegrated cellular tissue between them. The Myzodendron, having finally arrived at its full growth, a time probably coincident with, if not dependent upon, the period when the Fayus cannot supply it with sufficient nutriment, falls away and leaves a cup still attached to, or rather terminating the branch of a Beech (Plate CVI. f. 13) whose inner surface is channelled with radiating fissures and these again crossed by the concentric rings of the wood.

This process of germination is probably similar to what is pursued by many Loranthaceous plants, and is rudely represented by M. Korthals, as occurring in some Javanese species of this Order.

The resemblance between the sheathed radicle of Loranthus and Viscum and a coleorhiza was first pointed out by Mirbel, but hardly admits of a strict comparison of this order with Endorhizeæ in this respect, any more than the conferruminated cotyledons of this species are to be compared with the one large cotyledon of the true Monocofyledones, for in Viscum the cotyledons equally enclose a cavity containing the plumule, though they are not combined. The sheath of the root of Loranthacece appears a peculiar organ, especially adapted to the wants of the plants in which it occurs.

So very highly organized a nature of the embryo renders it probable that germination takes place very soon after the fall of the seed, or perhaps even before. It is remarkable too, that the operation proceeds in summer and exposed to the full light of day, there being no viscous substance to protect the embryo. I have described the radicle as descending from the seed to its future point of attachment, but here, as in Viscum, it is immaterial to which surface of the branch the embryo is approximated, the radicular extremity being invariably directed towards the axis. In a dried specimen of M. quadriforum I have found a seedling plant fully estabbshed on its parent. The frequent curving of the caulicule also, immediately after the protrusion of the radicle, is highly curious, the seed being loosely suspended by its filamentous appendages, and thus presenting no fulcrum or point of resistance, in attempting to overcome which, such a flexure might be induced. It is worthy of remark that both these functions, so closely resembling instinct in the lower animals, are characteristic of an embryo of more complex structure than any with which I am acquainted.

The absorption of nourishment from the albumen takes place through the cotyledonary extremity, which is retained in the perisperm, and by the time the radicle has gained the bark of the tree, the fecula of the albumen is wholly absorbed. This transfer of nourishment to such an extent, effected simply by the contact of two cellular membranes, only one of them being endowed with life, is a proof that in vegetables no very highly complicated tissues are required to conduct a very subtile chemical operation.

The bark of the Beech becomes detached from the subjacent wood prior to its complete penetration by the Myzodendron; the intrusion itself is by no means a mechanical operation, there can be little or no pressure exerted by an embryo suspended as tins is, it must be effected by the corrosion of the cortex which simultaneously produces a separation of the bark from the wood, materially facilitating the progress of the radicle.

I have mentioned that the duration or period of life allowed to the Myzodendron, is probably determined in some degree, by the effect it produces on the plant it infests; the latter being of slower growth, is sure at some period to rid itself of the intruder. Thus, the weight of the parasite being considerable, and exerted upon the branches