PLATE XX. 



Pifius Strobus. 



Fig. 2i6. The sexual nuclei just before coming into contact. Note depression, 

 in egg-nucleus. X i40' June 17, 1899. 

 217-223, a. Various appearances presented by the conjugating nuclei. It 

 will be borne in mind that these figures are so placed that the major 

 axis of the archegonia in which they occur would be parallel with the 

 longer axis of the plate. As a rule the sexual nuclei differ structurally 

 in size only. X 140. 



223. b. Another section through the egg-nucleus shown in fig. 223, a. There 

 is a greater difference in the size of the conjugating nuclei than would 

 appear in fig. 223, c, which is cut obliquely through the egg-nucleus. 



X 140. 



224. An early prophase in the first division following fecundation. Show- 

 ing early separation of chromatic from achromatic substance. X 472. 



225. A slightly later stage. The cytoplasm caught between the two nuclei 

 has collected into spherical masses. X 472- 



226. A still later stage in the formation of the two chromatic spiremes. 

 X472. 



227. A still later stage in which the paternal chromatic spireme has taken 

 up a position near the maternal spireme, and a few delicate achromatic 

 threads have made their appearance in the neighborhood of these 

 spiremes. The nuclear membranes are still present, but have broken 

 down at several points. X 472. 



228. A later stage. The nuclear membrane has entirely disappeared ; the 

 spindle fibers have increased in number ; and the rearrangement of 

 the achromatic, nuclear reticula into granular threads is ver^- apparent. 

 X472. 



229. More advanced stage in the formation of the spindle. The spindle is 

 distinctly multipolar in origin. X 472. 



( 194) 



