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NOTES ON THE STRUCTURE OF TMESIPTERIS. BY A.
VAUGHAN JENNINGS, F.L.S., F.G.S., Lecturer on Comparative Anatomy to the Birkbeck Institute ; and KATE M. HALL. Plates I. to V.
[Read APRIL 27, 1891.]
MHE genus Tmesipteris comprises one, or perhaps two species, of
1 Vascular Cryptogams found only in South Australia, Tasmania, New Zealand, and the South Pacific Islands. Its affinities to Psilotum have long been recognised, and the two genera have been classed together by systematic botanists. No complete account of its anatomy has, however, been written, and no details of its structure have, so far as we are aware, been published in English. Such being the case we have thought it might be of service to put together some notes on material collected in New Zealand in 1890; though the following account is by no means exhaustive, and no detailed comparison with allied types has been attempted. If no other purpose is served by the present communication it may at least call the attention of New Zealand botanists to the interesting points yet to be decided with reference to the plant.
B.I.A. PROC., SER. III., VOL. II.
Tmesipteris forsteri was so named by Endlicher in 1833: and is probably identical with T. tannensis, Bernh. Other so-called species differ only in slight and variable characters. It ranges through New Zealand, New Holland, New Caledonia, Tasmania, and South Australia.
The plant consists of a slender axis which grows among the rootlets covering the trunks of such tree ferns as Dicksonia antarctica and Hemitelia smithii, and then comes to the surface and forms pendent leaf-bearing shoots. There are no true roots. That part of the axis which penetrates the mass of fern-rootlets, and which for convenience we have referred to as the rhizome, may be more or less branched. The aerial part is almost always unbranched; and when dichotomy occurs it has probably no greater morphological significance than the bifiurcation of a fern rachis. Towards the distal end of the leafy shoots the single, sessile leaves are replaced by pairs of leaves carried out from the stem on a short lateral axis, and bearing on the upper side at the point of junction a bilocular sporangium. (Plate I.)
As already stated, the axis of the plant consists of two parts; one, which may be termed the rhizome portion, growing amongst the root-fibres of tree-ferns, and the other, or stem portion, hanging free and developing leaves. The rhizome portion near the surface of the trunk averages about 4 mm. in diameter, and is of a brown colour: it often gives off short lateral outgrowths apparently incipient or rudimentary branches, seldom more than inch long, terminating in blunt, rounded apices. The deeper portions are more slender, more branched, and covered with a thick layer of long hairs often longer than the diameter of the axis.
The stem portion is more angular in section, and pale green in colour; it tapers gradually toward the apex. The rhizome part passes gradually into the stem part without any sudden change, and it is difficult to make any morphological distinction between the two structures.
1 Endlicher, Prodromus Floræ Norfolkicæ.
? A variety is occasionally found on the ground, but the position of the rhizome in relation to surrounding objects in those cases does not seem to have been recorded.
M. Bertrand' terms the rhizome portion the stipe, and the stem portion a rameau souche : the intermediate part, or rameau rampant, he regards as having the value of un cladode de stipes. In the following notes we have referred simply to the “rhizome" or " rhizome portion," and "stem” or “stem-portion,” without entering into the question of their morphological value.
The Epidermis consists of a single layer of cells, approximately square in transverse section, but about four times as long as wide. Those of the rhizome portion have the outer wall coloured a bright yellow-brown, and often give rise to tubular hairs composed either of one cell only or of two cells, a long one on a short basal cell.
In the more deeply-seated parts of the rhizome the hairs are long -often longer than the diameter of the axis—closely set, and with protoplasmic contents. Those which are unbroken show a bent extremity similar to that of most root hairs, but we have not been able to trace any connexion between them and the rootlets of the tree-fern. It is possible that these hairs absorb nourishment from the earth enclosed among the rootlets of the tree-fern on which the plant grows, though some features, noticed below, would lead one to suppose that the plant is in part indirectly nourished.
The hairs are absent in the stem portion; and here the outer wall shows a very peculiar thickening, due to the presence of transverse and oblique bands which anastomose so as to form a reticulation on the surface. These thickened lines are strongly marked, but do not project down into the cavity of the cell in ridges to the same extent as in the leaf (Plate II., fig. 14). A distinct and thick cuticle covers the outside, and well marked cuticularized layers are present through the rest of the cellulose wall. Protoplasm and starch granules are present in the epidermal cells of both parts of the axis. Stomata are present, though not frequent, on the stem : they are of the same kind as those of the leaf, but circular, and the transpiratory chamber is narrow.
The ground tissue of the axis is of rather remarkable character. In the rhizome the cells are four or five times as long as broad, with horizontal or oblique end walls ; in transverse section circular or polygonal, showing distinct thickening (often collenchymatous), and a very evident middle lamella.
Both lateral and terminal walls are covered with bright spots of varying size, some of which are no doubt perforations. Transverse
| Annales Botaniques du Nord de la France, 1882.