Page:The Botany of the Antarctic Voyage.djvu/322

290 infested by this genus, will be described voider M. bracliystacltyum, where only I have been able to watch that opei'ation. The present species follows the same course, I presume, judging from the appearance of a fully established parasite.

The anatomy of the stem and branches of M. punctnlatum not only differs widely from that of M. brachystacliyum, but of most other Dicotyledonous plants ; its axis being wholly occupied by very dense fibres apparently of woody tissue, and presenting there no trace of the cellular tissue, which is constantly present in such plants as increase by annual layers. The bark of the young branches is thick and spongy and a transverse section presents the following structure. 1st. A very delicate but firni cuticle, striated externally with lines of extreme tenuity. 2nd. Immediately beneath this is a cellular tissue forming the epiphlceum. 3rd. A series of cavities occupy the circumference of the bark; they are what have been called in other plants respiratory cavities, and correspond each to one of the tubercles on the surface of the stem ; the cuticle is depressed immediately over the centre, where a very evident stoma is situated. 4th. The cellular tissue forming the mesophloeum is hexagonal, thick-sided, and very often full of a green chromule. I have seen no raphides in any of the species. 5th. The liber contains a series of isolated bundles of delicate fibres (Plate CVII.f. 9. a.) frequently, for some part of their length, protected by cells of great density, such as may be seen in the Lime and Antarctic Fagi. The proportion of fibrous tissue to the thickness of the bark is very small, and the fibres composing it exceedingly slender. Between this and the scalariform tissue lies a very thick layer of loose hexagonal cellular tissue, formed of membranous utricles, which are discoloured and compressed immediately around the annual layers. 6th. The greater portion of the old stem, all that part which, in Dicotyledonous wood, is usually occupied by pleurenchyma, is here wholly, or nearly, formed of elongated variously marked tubes, of almost equal diameter, they are white and diaphanous, dotted, ringed, transversely barred, or contain a spiral vessel, more or less broken (Plate CVII.f. 8,9 and 10, c). I have not observed simple or thick-sided tubes of pleurenchyma, true tracheae, or bothrenehyma, either in the inner portion of each annual layer, or in the usual position of the medullary sheath. 7th. The axis of the stem is formed wholly of a dense tissue of woody fibres (Plate CVII. figs. 8, 9 and 10 b.) the tubes all very small, inseparable, even after long maceration, and their walls so thick that it is difficult to trace the dark longitudinal liue which indicates their cavity which contains gramdes, though a dot in the centre of the transverse section of each fibre is very evident. This axis suffers no change after the first year's growth, and at that period may be seen to project wedge-shaped plates in the manner of medullary rays, into the scalariform tissue which it hardly divides.

The stems of this plant are, though hard in texture, very brittle, especially when dry, owing partly no doubt, to the fragile nature of the scalariform tissue, and probably still more to the very small quantity of parenchyma and the axis being formed of a denser substance than any other part. The ramification of this plant is highly peculiar, and uniformly takes place in the following manner. Each ultimate branch, when fully formed, Plate CVII. bis,f. 1, (and the plant itself, when consisting of a single uubranched stem) elongates no further in any succeeding year, but gives origin, towards its extremity, to five or six lateral amenta; these arise from the centre of a depression, bounded by a low cup-shaped sheath (Plate CIV.f. 1). All but a few of the upper of these amenta are floriferous ; they fall away after they have performed their functions, leaving a cicatrix on the ramulus, very visible even on the oldest stems, below every articulation. The upper empty amenta, however, (Plate CVII. bis, f. 1, a), elongate during the autumn, one or both of them, causing the ramification to be frequently either alternate or dichotomous; the bracteee are separated during this elongation, become recurved, fall off and leave a naked newly-formed branch (Plate CVII. bis, f.b.), fully developed by the month of September; toward the upper part of this, other amenta are formed and the process is repeated. The apex of the originally idtimate branch, now a stem, is reduced to a mere point (c), always discernible close to the articulation even of the oldest stems, though often very inconspicuous. Occasionally, three amenta are developed into branches, but this effecting a trichotomous ramification, is rare. The articulation of the stem in Myzodendron is therefore of a