134 



MOSSES AND FERNS 



CHAP. 



resulting chloroplasts remain close together with the nucleus, 

 in the centre of the cell. 



Owing to the small amount of chromatin in the nucleus, 

 the karyokinetic figures are small and the changes difficult to 

 follow satisfactorily. Enough can be easily made out, however, 

 to show that the process is in no way peculiar. There is first 

 a nuclear spindle of the ordinary form, and the resulting nuclei 

 assume the resting stage before dividing again. Each then 

 divides again, and the four nuclei move to points equidistant 

 from each other, and which are already occupied by the four 



chloroplasts. After this 

 is accomplished, cell walls 

 arise simultaneously be- 

 tween the four nuclei, 

 dividing the mother cell 

 into four tetrahedral 

 cells, — the young spores. 

 The wall of the mother 

 cell becomes thicker, and 

 in the later stages swells 

 up on being placed in 

 water, so that it interferes 

 a good deal with the 

 study of the spores in 

 the fresh condition. As 

 the spores ripen they 

 develop a thick exospore, 

 which is yellow in colour 

 and irregularly thickened 

 in A. IcEvis, and in A. 

 fusiforniis black and covered with small tubercles. The chloro- 

 phyll disappears and the spore becomes filled with oil and other 

 food materials. The spores remain together until nearly ripe. 

 The elaters, if this name can properly be applied to the sterile 

 cells, at maturity consist of simple or branching rows of cells, 

 which in some cases arise from the division of a single one ; but 

 more commonly, at least in A. IcEvis, where they branch, it is 

 probable that they are to be looked upon as merely fragments 

 of the more or less continuous network of sterile cells. The 

 contents mainly disappear from the older elaters, and their 

 walls become thick and in colour like the wall of the spores. 



Fig. 63. — Spore division in A. fiisiformis, optical sections 

 of living cells, X 600. 



