174 Lawson . — The Gametophytes and Embryo of 
that the fibrils of the first cleavage spindle are differentiated out of nuclear 
substance. The following observations I think will show that these fibrils 
are of cytoplasmic origin. These cytoplasmic masses first appear very soon 
after the ventral canal cell is organized, and while the egg-nucleus is com- 
paratively small. The cytoplasm surrounding the young egg-nucleus becomes 
more dense, forming a more or less definite zone, much as in the early spindle- 
formation stages in the Angiosperms. This zone, however, owing to the 
very rapid growth and distension of the nucleus, becomes interrupted at 
intervals. As a result of this continued rapid growth we find, instead of 
a zone, numerous patches or masses of cytoplasm which become quite 
separated from one another, and which stain more deeply than the surround- 
ing cytoplasm. These dense masses — which soon show a finely fibrous 
structure — being in contact with the nuclear membrane, offer a resistance to 
the growth of the nucleus. The osmotic pressure within— -which no doubt 
causes the enlargement of the nucleus — forces the membrane between these 
dense masses, and almost completely envelops them. The result is that 
the contour of the nucleus becomes interrupted by several infolding pockets, 
each of which contains a dense mass of cytoplasm which is distinctly fibrous 
in structure. On account of their distribution they could be studied to 
much better advantage in cross- than in longitudinal-sections. A characteristic 
appearance of a cross-section of a nucleus at this time is shown in Fig. 31. 
Very similar pockets of cytoplasm have been noted and figured in 
Pinns by Ferguson (’ 05 ) and in Tsnga by Murrill (’ 00 ), but neither of 
these writers mentions the fact, although it is clearly demonstrated in their 
figures, that a considerable amount of cytoplasm is carried into the egg- 
nucleus at the time of the fusion of the sex nuclei. Indeed, both of these 
writers describe the spindle fibrils of the first mitosis of the pro-embryo as 
originating from transformed nuclear substance. The chromatic contents 
of the egg-nucleus at maturity are quite like that of Pinus which 
has been described by Blackman (’ 98 ) and Ferguson (’ 05 ), as is shown 
in Fig. 30. Immediately before fusion the chromatin becomes collected 
near the centre of the nucleus in the manner indicated in Fig. 32. Although 
the actual first contact of the male nucleus with the egg-nucleus was not 
observed, the stages immediately following were found in several prepara- 
tions. One of these stages is shown in Fig. 33. It became evident from 
this figure that there is no resting period of the fusion-nucleus, for the first 
segmentation spindle is already in process of formation. Although the 
chromosomes could be observed quite easily, it was impossible to dis- 
tinguish the male group from the female. As shown in Fig. 33, the first 
spindle of the pro-embryo is formed within the area bounded by the mem- 
brane of the egg-nucleus. There seems little doubt that its fibrils are formed 
out of the dense masses of cytoplasm carried in by the male nucleus, and not 
out of nuclear substance. 
