EQUISETINE^ 



A77 



characteristic nuclear plate. The separate nuclear spindles 

 finally converge more and more, until finally they unite into a 

 more or less definite large bipolar spindle with the nuclear plate 

 at the equator (Fig. 279, C). Before the final division takes 

 place, the sporogenous cells become completely rounded off, 

 and are embedded in a mass of nucleated protoplasm (Fig. 

 280, A) derived from the tapetal cells, but also in part from 

 some of the archesporial cells vi^hich do not develop into spores. 

 Fig. 279 shows the successive stages in the process. During 



Fig. 279. — ^A, Group of four sporogenous cells of H, telmateia, X400; B, C, first mitosis 

 in E. Umosum (after Osterhout); B, shows the multipolar spindle; D, E, second 

 mitosis in E. telmateia. 



the division of the primary nucleus there is an evident cell plate 

 formed, but no division wall. 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. 

 279, D). 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. 279, D). In either case the 

 resulting nuclei arrange themselves at equal distances from the 



