PLATE XVII. 



Pinus Strobus unless otherwise indicated. 



FIGS. 185-186. Later stages in the prophase of the division of the central cell. 

 X472. Fig. 186, Pinus austriaca. 



187-188. Disappearance of the nuclear membrane and establishment of the 

 achromatic spindle. The spindle now lies wholly within the area pre- 

 viously occupied by the nucleus. X 472. 



189. Cross-section of the nucleus of the central cell just as the chromo- 

 somes are undergoing longitudinal splitting at the equatorial plate. 

 X472. 



190-197. Separation of the half chromosomes and formation of the daughter- 

 nuclei. X 472. Figs. 192 and 195, Pinus austriaca. These figures 

 show some of the variations occurring in the mitotic figure for this 

 division, and the corresponding variations in the structure of the 

 nucleus of the ventral canal-cell. Figs. 190, 191, 193 and 196 are very 

 interesting, showing how some at least of those ventral canal-cells in 

 which no definite nucleus is organized have arisen. Figs. 192, 194 

 and 195 are also interesting as leading to the formation of a normal 

 nucleus within the ventral canal-cell. It will be noted that this spindle 

 is always monopolar at its lower extremity and usually broadly multi- 

 polar at the opposite end. Fig. 192 is the only instance observed of a 

 sharply bipolar spindle. The egg nucleus is larger from the very 

 first than the nucleus of the ventral canal-cell. 



(188) 



