LIFE HISTORY OF PINUS 97 



which is muhipolar at one extremity and monopolar, or nearly 

 so, at the other (figs. 187, 188). A similar figure is also organ- 

 ized in the mitoses which occur in the development of the pol- 

 len-grain, and at an early stage in the division of the generative 

 nucleus in the pines, as already described in this paper ; and it 

 is suggested that such a figure may be characteristic, at least in 

 the higher plants, of those indirect divisions which result in the 

 formation of nuclei or cells of unequal size. 



The chromosomes, when oriented at the nuclear plate, are in- 

 variably in the form of U's or Vs. Blackman states that they 

 are straight rods but he does not so figure them. The cell- 

 plate, during the early stages in its formation, lies midway be- 

 tween the developing nuclei, but when the daughter-nuclei are 

 fully formed, the nucleus of the oosphere is, as a rule, farther 

 removed from the cell-plate than is the nucleus of the ventral 

 canal-cell. A prominent cell-plate is formed and the plane of 

 cleavage separating the ventral canal-cell from the egg becomes 

 evident in many instances before the disappearance of the 

 spindle. As Chamberlain ('99) has shown, the lower portion of 

 the spindle at this time is ordinarily convex, while the part 

 within the ventral canal-cell is concave (figs. 195-197, plate 

 XVII, and 200, 201, plate XVIII). 



I was able in several preparations similar to that illustrated 

 in fig. 191 to count the number of chromosomes, and twelve or 

 thirteen were found in both groups instead of eight as counted 

 by Dixon ('94). 



The Ventral Canal-cell. — According to my observations, a 

 definite wall, separating the canal-cell from the egg-cell, is 

 always formed in Pinus. Coker has made the interesting 

 observation that no wall is developed in Podocarpus, the nucleus 

 of the ventral canal-cell lying free in the egg.^ As a rule the 

 nucleus of the ventral canal-cell in Pinus does not present a 

 normal appearance, but shows signs of disintegration very early 

 in its history. It is doubtful, in some cases, if a nuclear mem- 

 brane is ever formed, and there are probably instances in which 

 fusion of the chromosomes never takes place at all. The kar- 

 yokinetic structure shown in fig. 193 would very presumably 



^ See note at close of Appendix. 



