Fertilization in Pinus Sirobus 451 
out, not only along the line of contact of the two nuclei, but 
from their entire outer surfaces as well (Fig. 55). Blackman 
found that, while the chromatic portions of these nuclei 
remained distinct in Pinus sylvestris , the nuclei fused at an 
early stage in the prophase of the division. There is, 
apparently, no such fusion of the sexual nuclei in Pinus 
Sirobus ; but the entire membrane of each nucleus disappears 
during an early prophase of the mitosis, and the contents of 
the nuclei lie free in the cytoplasm of the egg. 
The spindle-fibres continue to increase 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 spirems. 
They probably feed the growing spindle, some of them, 
doubtless, being directly transformed into spindle-fibres. The 
chromatic bands have now become perfectly homogeneous. 
Before their segmentation, the very irregular, multipolar poly- 
arch spindle has become a multipolar diarch (Strasburger, 
’00) 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. 56-58). 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 the female nucleus (Plate XXV, Figs. 58 and 59). This 
appearance, however, may be only accidental, 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 spirems, and can still be clearly 
made out during the early development of the chromo- 
somes (Figs. 59 and 60). When the chromosomes are 
oriented at the nuclear plate, the maternal and paternal 
elements can no longer be distinguished (Fig. 6j ). One 
H h 
