Graham: Conocephalum conicum 619 



2g,ji). During the continued growth of the sporogonium both 

 the foot and capsular portion expand, so that a definite constric- 

 tion appears {^Jigitres 2y, 2g^ j6). This constricted portion is the 

 part which later gives rise to the stalk. 



In the capsular portion cell division soon gives rise to a single 



r 



superficial layer of cells which is distinguished from the tissue 

 within, in that its cells are larger and less rich in protoplasm and 

 therefore stain less deeply. This superficial layer becomes the 

 wall of the capsule, while the deeply staining inner tissue, the cells 

 of which have now become arranged in longitudinal rows, is the 

 sporogenous tissue {^figures ^7, j(5, jp). At this time the sporo- 

 gonium fills the cavity of the venter, pressing against its wall. 



Certain cells of the alternate rows of the sporogenous tissue 

 become larger than those lying between them, are richer in pro- 

 toplasm, and have larger nuclei. These are the mother-cells of 

 the spores {^figure ^7). Figin^e jj shows a slightly older stage. 

 These enlarged cells are separated from those surrounding them, 

 become rounded and undergo a period of growth, after which each 

 divides into four tetrahedral spores {^figure 46). 



By the time the tetrads are formed the cells that are to form 

 the elaters have elongated considerably as is shown in figure 48^ 

 but the characteristic elater-form does not appear until after the 

 spores have become mature in the autumn. 



The sporogenous tissue in the capsule of Conocephahtm^ Preissia, 

 and Marchantia is arranged in longitudinal rows. In the two 

 former plants some of the cells in alternate rows enlarge, separate 

 from the adjacent cells, and become the spore mother-cells, each 

 of which divides into four tetrahedral spores. In the last-named 

 plant, the sporogenous cells divide into groups of four or eight 

 cells each, which always retain their identity as groups, each cell 

 of the group ultimately dividing to form four spores. It has long 

 been known that the spores of CoiiocepJiahim conicum germinate 

 while still within the capsule {^figure §4). The spores of Mar- 

 chantia and Preissia do not germinate until after they have escaped 

 from the capsule. 



During the development of the sporogonium prominent changes 

 take place in the surrounding tissue of the gametophyte, so that 

 at the time of its maturity, it is enclosed not only in the calyptra, 



