454 MOSSES AND FERNS chap. 



somewhat carefully followed in E. telmateia. After the com- 

 plete number of cells has been formed in the archesporium, and 

 before the tapetal cells are broken down, the sporogenous cells 

 are divided into groups which begin to separate from each 

 other. With the enlargement of the sporangium and the 

 breaking down of the inner tapetal cells these masses become 

 isolated, and are very easily removed from the sporangium (Fig. 

 240, A). They usually consist of four cells, which in water 

 swell up somewhat. In a fresh condition they appear quite 

 colourless, but the cytoplasm is densely granular. The nucleus 

 is very large and appears quite transparent with one or two 

 distinct nucleoli. In material treated with osmic acid, what 

 appeared to be the centrospheres were seen, but not very 

 clearly. In microtome sections of about the same age (Fig. 

 240, B) the numerous rod-shaped chromosomes were very evident, 

 but their number could not be determined. The nucleolus is 

 conspicuous, and on one side, in a slight depression in the 

 nuclear membrane, are the two centrospheres. These latter 

 were not always perfectly evident, but are probably always 

 present. The radiating lines about them were not seen. 

 Before the final division takes place, the sporogenous cells 

 become completely rounded off, and are embedded in a mass 

 of nucleated protoplasm (Fig. 241, A) derived from the tapetal 

 cells, but also in part from some of the archesporial cells which 

 do not develop into spores.-^ 



Fig. 240 shows the successive stages in the process. 

 During the division of the primary nucleus there is an evident 

 cell plate formed (Fig. 240, E), but no division wall. The 

 period at which the centrospheres divide could not be made 

 out, but by the time the division is complete each nucleus is 

 provided with two, which are decidedly smaller than the 

 primary ones. During this first division there is probably a 

 reduction in the number of the chromosomes, as in Osmunda. 

 At any rate the number is evidently much smaller during the 

 metaphases of the second nuclear divisions (Fig. 240, F). The 

 second divisions are the same as the primary one, and the 

 planes of the two nuclear spindles may either be parallel or at 

 right angles (Fig. 240, F). In either case the resulting nuclei 

 arrange themselves at equal distances from the centre of the 

 cell, and the connecting filaments are formed between them. 



^ Bower (15), p. 500. 



