502 



MOSSES AND FERNS 



CHAP. 



Kraussiana (Fig. 265, A) a radial section of the young 

 sporangium shows a very regular arrangement of the cells, with 

 a single central archesporial cell (the nucleated cell of the 

 figure). This evidently has arisen from a hypodermal cell of 

 the central row, and from it is already cut off by a periclinal, 

 an outer cell. The whole closely resembles Goebel's figures 

 of kS. spinosa. A comparison with older stages indicates that 

 from this central cell alone the sporogenous cells are produced, 

 as in Lycopodium selago. The outer row of cells does not 

 divide by periclinal walls, and from the first forms an extremely 



A 



J--L 



Fig. 263. — Selaginella Kraussiana (A. Br.). Development of the microsporangium, radial sections. 

 A-C, X500 ; D, X235. The nuclei of the archesporial cells are shown. L, The leaf subtending 

 the sporangium. 



distinct layer. The first cell cut off from the archesporium 

 divides again by a periclinal wall (Fig. 265, B), and the inner 

 cell forms probably the first tapetal cell, although in some 

 cases it looks as if this cell took part in the formation of 

 spores. The archesporium undergoes repeated divisions to 

 form the sporogenous tissue, and finally the layer of cells 

 between these and the primary wall divides by periclinal walls 

 to form the tapetum, which here remains intact until the spores 

 are nearly or quite mature. The formation of the stalk is 

 the same as in Lycopodhnn. 



