Page:The Botany of the Antarctic Voyage.djvu/333

Falklands, etc.] /. 12, which is taken from a branch of Fagus six years old, it will be seen that the ducts, dotted and otherwise marked vessels are large and abundant, and that the chief difference between /. 12, and a similar section of one wedge of Myzodendron brachystacliyum f. 6, lies in the scalariform vessels being disproportionately abundant in the latter, and not being scattered amongst the pleurenchyma.

Ramification. In this, as in M.punctulatum, the terminal internodes bear, towards their upper part several buds, each opposite the axil of a leaf; of these the leaf-buds elongate and become new, permanent internodes; the flower-buds fall away. In the former species (Plate CVII. iis,f. 1) the flower-buds were near the apex of the internode, and two frequently becoming developed into branches, the ramification was consequently dichotomous. In M. bracliystachjum (Plate CVII. bis, f. 7) the flower-buds are generally the upper, and the ramification hence alternate.

The vaginas enclosing the unprotruded buds are vertically two-lipped, and formed from the bark which encloses a large cavity communicating almost with the axis of the stem where the bud is developed. The dehiscence is spontaneous, before the included organ has advanced sufficiently to force a passage. The relation of these parts to those of a germinating embryo is clear ; the cavity in the internode containing the bud is analogous to that in the cotyledonary extremity of the embryo including the plumule, whose course in germination is thus imitated by the buds as often as the plant developes them.

Germination. I have been able to watch the progress of germination in this species and to follow the course of the radicle from the time of its leaving the pericarp, till it has fully established itself upon the tree it affects.

Several of the ripened seeds, still enclosed in their pericarps, are generally detached together from the parent plant, they adhere by their viscid filaments and are carried by the birds, winds, or other natural causes, from one tree to another, where they may often be seen hanging entangled amongst the leaves and twigs. The grain is placed almost in contact with the stem ; it is immaterial to which surface. As I have not seen young Myzoiendrons attached to old trunks and branches, I presume the young plant can only pierce a comparatively newly formed bark. The elongation of the caulicule pushes before it the disk and style, which fall away, and the radicle always escapes at this point and protrudes beyond the pericarp, to which the embryo remains attached until the parasite has gained a firm lodgment on the tree. The embryo now generally becomes curved, the elongating caulicule seeking the nearest point of the beech, which it finally reaches. At this period the cotyledons, distinctly swollen, are still contained in the shrivelled albumen, and a very evident notch marks their point of union (Plate CVI. /. 5). The radicle now expands like the mouth of a trumpet, is concave and has become a compound body, consisting of three distinct parts, 1st. a membrane continuous with the surface of the caulicule, which expands horizontally over the cuticle, is glutinous, and is the first inmiediate cause of adhesion between the bark and the parasite. 2nd. A thick fleshy sheath, whose convex margins touch the bark. 3rd. A cushion-shaped body in the axis of the radicle, which is pressed against the bark and is destined more immediately to convey nourishment from the tree to the future full-grown parasite. At Plate CVI. /., is a germinating seed, with the cotyledonary extremity still enclosed in the albumen, and the radicular expanded as it appeai-s on reaching the bark ; /. 5 represents the same attached, with the albumen removed, shewing the notch of the cotyledons.

If a longitudinal section of the "embyro be now made, (as at Plate CVI./. 6) there will be seen, 1st, at the base of the cavity in the cotyledonary extremity, two excessively minute green bodies, which, at a later period, become developed into the first pair of leaves, are pointed upwards towards the notch at the union of the cotyledons, and escape by the rupture of the membranes that enclose them : 2nd. spiral vessels descending from the base of these which are lost in the cellular substance of the cushion-shaped body (Plate CVI. /. 7) : 3rd, a longitudinal line indicating a future separation of the cotyledons and outer substance of the embryo, the latter forming an integument that includes the plumule, cushion-shaped body and its surrounding sheath. This central mass, included between the plumule above and base of the cushion below, is the growing portion of the future plant, all