INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 989 



of cells are arrested in their growth, lose their abundant protoplasm, 

 and divide only into elongated tubular cells. These are the sterile 

 cells or trabeculjB. The sporogenous cells, continuing to grow and 

 retaining their protoplasm, divide only by transverse se^^ta. In the 

 macrosporangium the fertile cells of the archespore undergo no 

 further divisions than those which result in the formation of the 

 mantle-cells. 



A close analogy may be drawn between the development of the 

 macrospore of Isoetes and that of the embryo-sac of jihanerogams, 

 the chief difference being that the mother-cells are, in the former case, 

 numerous, while in the Litter case there is usually only one. In the 

 Coniferae the mother-cells of the embryo-sac (archespore) originate 

 from the hypodermal layer, and their depression in the interior of the 

 macrosporangium corresjjonds to that in Isoetes. In both cases the 

 embryo-sac consumes the surrounding tissue. Occasionally, in gymno- 

 sperms, there is more than one embryo-sac mother-cell ; but they are 

 not then, as in Isoetes, separated by a sterile tissue (the trabecul£e). 

 In angiosperras and in Ephedra, the archespore has been shown, by 

 Warming and Strasburger respectively, to consist of a layer of cells, 

 as in Isoetes. A similar comparison may be drawn between the deve- 

 lopment of the microsporangium of Isoetes and that of the pollen-sac 

 of phanerogams. 



In the Bryineae and Sphagnace^ the archespore consists of a layer 

 of cells ; and this is also the case in certain Hepaticfe, certainly in 

 the Anthoceroteaj ; while, in Biccia, there is no separation into a sterile 

 part of the capsule and an archespore. 



Muscineae. 

 Structure of the Stem of Mosses.*— M. I'Abbe Hy has carefully 

 studied the structure of tlie stem of mosses belonging to the family 

 Polytrichaceae, especially of the species Atnchum iindulatum and Poly- 

 trichum commune. The following is a summary of the most important 

 results : — 



1. The anatomical structure of the stem in this family is more 

 complex than has hitherto been supposed, and includes six well- 

 marked different kinds of tissue. One of these, termed by Schimpcr 

 the woody tissue, is itself made up of three characteristic regions. 



2. The stem is not miifurm, nor reducible to a single type. 

 In one species, for example, Poli/trichtm commune, very important 

 differences of structure may be observed at different heights, which 

 may be arranged under tliree kinds, connected by intermediate forms. 

 Even the external configuration varies, from cylindrical to triangular 

 prismatic, and irregularly polygonal towards the summit. The dia- 

 meter increases progressively, from ^ mm. to 1] mm., that is, about iu 

 the proportion of 1-4. 



3. A cortical investment, similar in appearance to that which has 

 long been known in the case of the Sphagnaceic, and of which somo 

 traces arc also ftnnul in the genus Philiniolis, exists also well developed 

 at the base of the stem of our indigenous Poli/lrichums, and even of 



* 'Dull. Sof. Bot. Fmiicc,' xxvii. (ISSO) p. IOC. 

 VOL. III. 3 U 



