LIPE HISTORY OF PINUS II7 



nucleus disappears during an early prophase of the mitosis, and 

 the contents of the nuclei lie free in the cytoplasm of the Qgg- 

 I have never found in the process of fertilization in Pimis any 

 structure that could properly be designated as a fusion-nucleus. 

 This is exactly comparable with what has been observed in the 

 ovum of some animals, but has not been previously described 

 for any plant. It might be noted that this conclusion was 

 reached very early in the course of these studies, when the 

 writer had read but little along cytological lines, and was not 

 aware either that such a process was unknown in plants, or that 

 a similar conduct of the sexual nuclei had been described by 

 some writers on the animal side. 



As the mitosis proceeds, the spindle-fibers continue to in- 

 crease in number, becoming even more delicate in structure, 

 and losing their granular appearance. The long, now quite 

 delicate, but still granular, achromatic threads of the nuclei are 

 very numerous, and many extend into the areas occupied by the 

 chromatic spiremes. They probably feed the growing spindle, 

 some of them, doubtless, being directly transformed into spindle, 

 fibers. The chromatic bands have now become perfectly homo- 

 geneous. Before their segmentation, the very irregular, multi- 

 polar polyarch spindle has become a multipolar diarch spindle ; 

 and the achromatic substance not used in spindle-formation 

 has been gradually resolved, from the periphery of the nucleus 

 inwards, into a granular, or finely reticulated structure, which 

 later merges into the general cytoplasm of the egg (figs. 229- 

 231). When the spindle has become a true multipolar diarch, 

 it frequently consists of two nearly equal parts, which seem to 

 belong respectively to the male and female nuclei (figs. 231 and 

 232, plate XXI). This appearance, however, may be onl}^ acci- 

 dental, as the great irregularity which characterizes this spindle 

 in the first stages of its formation renders such an origin of the 

 two halves of the nearly completed spindle very problematic. 



Two chromatic groups are distinctly recognized at the time 

 of the segmentation of the spiremes and can still be clearly made 

 out during the early development of the chromosomes (figs. 

 232 and 233). When the chromosomes are being oriented at the 

 nuclear plate the maternal and paternal elements can no longer 



