GYMNOSPERMS. 167 
Although the male nucleus is almost enclosed by the female, actual 
fusion, according to Blackman, does not take place immediately, since 
the membrane of the male nucleus is intact (Fig. 69, B). The mem- 
brane soon disappears, but the chromatin of the two nuclei does not fuse 
at this stage and no resting fusion nucleus is formed. With further 
development the chromatin of each nucleus will give rise to a group of 
chromosomes, which become arranged upon the spindle of the first 
division after fecundation where they are seen to be split longitudinally 
(Fig. 69,C). As has been pointed out for Ginkgo (Fig. 67, C, D) the 
spindle seems to arise entirely within the limits of the female nucleus. 
In Pinus laricto, according to Chamberlain, after the male nucleus 
is within the nucleus of the egg, the chromatin of the two pronuclei 
appear as two distinct masses in the spirem stage. Murrill finds that 
in Zsuga canadenszs both nuclei are in the resting condition when 
actual fusion begins, but he seems to be of the opinion that the identity 
of the male and female chromatin can be traced until the division of 
the fusion nucleus, as will be seen from the following : 
The chromatin of each nucleus collects in the form of a thick knotted thread 
near the center of the separating partition, and the two masses remain distinct 
until the spirem bands begin to segment. Just before the spirems are formed 
the separating membranes disappear and the nuclear cavities become united. 
The spindle then arises in a multipolar fashion between and among the two 
masses, twelve chromosomes being supplied from the chromatin of the sperm 
and twelve from that of the egg, as described by Blackman for Pinus sylvestris. 
Ferguson finds in Pizus strobus that the two sexual nuclei do not 
fuse in the resting stage. The male nucleus imbeds itself in the egg- 
nucleus but does not penetrate its membrane. In each nucleus is devel- 
oped a chromatin spirem and an achromatic reticulum. The nuclear 
membranes now disappear, but the two chromatin groups remain 
distinct until the nuclear-plate stage (Fig. 68, D). 
The spindle of the first division following fecundation always lies between 
the conjugating nuclei and parallel with the outer, free surface of the sperm 
nucleus. It is multipolar in origin and is probably derived equally from the 
paternal and maternal nucleus. The spindle fibers appear to arise by a re- 
arrangement of the achromatic nuclear reticula, and are evidently not the 
expression of a special kinoplasmic substance, 
In the stage of the mature spindle of the first division following 
fecundation in Pinus austriaca, the species examined by myself, no 
distinction whatever could be recognized between male and female 
chromatin. 
