PLATE XXI. 



Pinus Strobus. 



Fig. 230. The spindle fibers have become more abundant and transverse segmen- 

 tation of the spiremes has occurred at some points. X 472. 



231. The spindle fully established having now assumed the form of a 

 multipolar diarch ; the two chromatic spiremes still perfectly distinct. 



X472- 



232. The two spiremes after segmentation; the two halves of the spindle 

 seem to indicate the maternal and the paternal portions of the mitotic 

 figure. X 472- 



233. Early stage in the formation of the chromosomes. The chromatic 

 elements still occur in two distinct groups, but position, alone, deter- 

 mines which are maternal and which are paternal. The segments can 

 not be structurally differentiated. X 472. 



234. The chromosomes being oriented at the nuclear plate. The distinc- 

 tion between paternal and maternal elements no longer evident. 

 X472- 



235. A cross-section through the nuclear plate just before the separation 

 of the chromosomes ; twenty-four segments are distinctly shown. 

 X472. 



236-23S. Some of the aspects presented by this mitotic figure during meta- 

 kinesis. X472. 



239. An anaphase of the mitosis. X472. 



240. A late anaphase of the division ; the poles terminate in granular areas 

 from which delicate threads extend into the cytoplasm ; some of the 

 nucleolar substance from the egg-nucleus still persists. X472. 



241. One end of the spindle in the same stage as the above ; the fibers which 

 radiate from the polar region of the spindle are very abundant and 

 stain deeply. X472. 



(196) 



