PLATE III. 



Fig. 24. The equatorial plate stage. Spindle definitely bipolar and reaching to 

 the ectoplasm. X Ij400. Pinus rigida. 



25, 26. The metaphase of the heterotypical division ; chromosomes irreg- 

 ular in outline and apparently much larger than in the late prophase. 

 X 1,400. Pinus Strobus. 



27-29. Anaphase of the heterotvpical division. The longitudinal split- 

 ting of the chromosomes has been very greatly delayed in some cases. 

 Such an appearance as that shown in fig. 29 is frequently met with, 

 the stretched arms of the daughter chromosomes extending nearly the 

 entire length of the spindle. X 1,400. Pifius Strobus. 



30. The chromosomes just after reaching the poles, as seen in looking 

 down upon the end of the pole. X 1,400. Pinus Strobus. 



31-34. Stages in the development of the daughter-nuclei. A definite 

 resting nucleus is formed at the close of the heterotvpical division. 

 X 1,400. Pinus Strobus. 



35. A late telophase in the first division, the daughter-nuclei fully estab- 

 lished. Delicate spindle threads still present, but no indication of a 

 cell plate. The wall of the microspore-mother-cell is beginning to 

 thicken centripetally. X 1,400. Pinus Strobus. 



36-37. Stages in the formation of the spireme for the second division. 

 X 1,400, Pinus Strobus. 



(160) 



