GAMETOPHYTE AND SPOROPHYTE. 



341 



the nucleus, giving rise to a succession of nuclear figures presented 

 by a definite but variable series of evolutions on the part of the 

 nuclear substance. This is indirect division of the nucleus, or 

 karyokinesis. Indirect division of the nucleus is the usual method, 

 and it occurs in the normal growth and division of the cell. The 

 nuclear figures which are formed in the division of the mother 

 cell into the four spores are somewhat different from those 

 occurring in vegetative division, but their study will serve to show 

 the general character of the process. 



679. Chromatin and linin of the nucleus. In figure 404 

 is represented a pollen mother cell of the May-apple (podophyl- 



Fig. 404. Fig. 405. Fig. 406. 



Pollen mother cell Spirem stage of nucleus.^ Forming spindle, 



of podophyllum, rest- nu, nuclear cavity ; , nu- threads from proto- 



ing nucleus. Chroma- cleolus ; SJ>, spirem. plasm with several 



tin forming a net- poles, roping the 



work. chromosomes up to 



(Figures 404-406 after Mottier.) nuclear plate. 



lum). The nucleus is in the resting stage. There is a network 

 consisting of very delicate threads, the linin network. Upon 

 this network are numerous small granules, and at the junction of 

 the threads are distinct knots. The nucleolus is quite large and 

 prominent. The numerous small granules upon the linin stain 

 very deeply when treated with certain dyes used in differentiating 

 the nuclear structure. This deeply staining substance is the 

 chromatin of the nucleus. 



