PLATE XVIII. 

 Pinus Strobus. 



Figs. 198-199. Some of the aspects presented by the ventral canal-cell. It is 

 doubtful in both of these cases if any nucleus has ever been organized 

 within the ventral canal-cell, and the chromosomes have not even 

 fused to form a spireme. X 472- 

 200-202. Later history of the ventral canal-cell and early stages in the 

 development of the egg-nucleus. The first indication of the primary 

 nucleolus is seen on the lower side of the egg-nucleus in fig. 202, and 

 the ventral canal-cell already shows marked signs of disintegration. 



X472. 



203-204. Later stages in the downward movement and growth of the egg- 

 nucleus showing growth of primary nucleolus. X 472. 



305. Mature egg-nucleus. The primary nucleolus is very large and vacuo- 

 late and several secondary nucleoli are scattered throughout the nu- 

 cleus. The structure of this nucleus varies greatly. This one was 

 selected not because it can be said to be any more typical than others, 

 but because it represents an average rather than an extreme condition 

 as to density of reticulum and number of secondary nucleoli. X 472- 



( 190) 



