ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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development of the bundles, the first elements to become differentiated 
are sieve-tubes, followed by the central tracheid of the xylem. Tho 
tracheids which are first differentiated are prismatic, with polygonal 
section, and are terminated by horizontal septa. 
In all the species examined, in the portion of the leaf which runs 
from the glossopode to its insertion in the rhizome, the sieve-tubes are 
united into a single zone, and constitute the greater part of the phloem- 
arc. In the section of the ligule and in that of the sporange, the xylem 
consists simply of tracheids of irregular thickness, constituting a net- 
work, the meshes of which are occupied by very thin-walled cells. 
Lycopodiacese.* — Prof. F. 0. Bower gives a sketch of the structure 
of this order of Vascular Cryptogams, and of its relationship to the 
extinct Lepidodendra. He states that while the latter, which varied 
among themselves to a considerable extent as regards details, correspond 
in their most important characters to the Lycopodium of the present day, 
they yet differed greatly from them in several respects, of which the most 
notable are their size, the presence of secondary thickenings in the stem, 
and the greater sexual differentiation as shown by the presence of two 
kinds of spore, male and female. 
Hymenophyllacese.f — Herr C. Giesenhagen has examined the sexual 
generation of several species of Hymenophyllaceae, especially H. caudicu- 
latum. The pro thallium of several species of Trichomanes is distinguished 
by the formation of gemmae, spherical cells elevated on the apex of a 
pedicel, which divide, and finally become detached from the pedicel, and 
develope into new prothalloid filaments. While the prothallium of 
Trichomanes is dioecious, that of Hymenophyllum is frequently monoe- 
cious. The prothallium of T. radicans may continue to grow for three 
years without producing antherids or archegones. 
In the spore-producing generation, while many species are rootless, 
others produce adventitious roots. Some species have barren and fertile 
leaves of different structure ; the sterile leaves are always simply pinnate. 
Most species of Trichomanes are distinguished by the occurrence in the 
stem of “ stegmata,” flat tabular cells containing a mass of silica in contact 
with their inner wall. A sclerenchymatous cortex is almost universal 
in the stem and root. Trichomanes microphyllum n. sp. belonging to the 
section Hemiphlebium, is the smallest known fern, with leaves not more 
than 7 mm. in length, each of which has a single terminal sorus. The 
stem is penetrated by a vascular bundle of the simplest possible constitu- 
tion, consisting of a single tracheid surrounded by four or five cambiform 
cells. The purpose of the conducting bundle in the Hymenophyllaceae 
appears to be to carry the nutrient material to the sori and other parts 
where it is required. The rootless species have root-like cauline shoots, 
which attach the plant, and serve for the absorption of nutrient material. 
While the stem-bundle is completely surrounded by a sclerenchymatous 
ring, in the leaf-veins the bundle is protected only by a layer of 
sclerenchyme above and below, and the nutrient material reaches it from 
the parenchyme of the leaf through the lateral openings. 
* Proc. Phil. Soc. Glasgow, xxi. (1890) pp. 158-72. 
f Flora, Ixxiii. (1890) pp. 411-64 (4 pis.). 
