No. 463.] STUDIES ON PLANT CELL.— VI. 461 
from both gametes maintain their independence and never fuse 
at the immediate time of fertilization. We have reason to 
assume, chiefly from zoólogical studies, that the paternal and 
maternal chromosomes of plants remain independent throughout 
the entire sporophyte generation and that no fusion takes place 
until the period of chromosome reduction at sporogenesis. If 
no sporophyte generation is present we should expect the fusion 
and reduction of the chromosomes to occur after the sexually 
formed cell had passed through a period of rest (for all reduction 
phenomena seem to require considerable time) unless there be 
actually such reduction during gametogenesis in the thallophytes 
as reported for Fucus and Saprolegnia. The morphology of the 
chromosomes is probably unchanged by the immediate act of 
fertilization. The fusion nucleus simply contains double the 
number of chromosomes present in each gamete nucleus which 
increases by so much the metabolic possibilities which lie in 
these structures. 
Besides chromatin the sperm brings into the egg a certain 
amount of cytoplasm. Some of this may be the substance of 
the blepharoplast or other kinoplasm associated with the nucleus 
but there is often besides considerable granular trophoplasm, 
sometimes with inclusions of starch and other food substances, 
and the male gamete of certain thallophytes contains a chroma- 
tophore. There is no reason to suppose that development 
especially characteristic of fertilization, the sporophyte genera- 
tion, has any relation to this trophoplasm with its food inclusions, 
excepting as' it may stimulate growth which is to be expected 
whenever organic food material is introduced into protoplasm. 
But we can hardly believe that the formative elements or the 
rudiments of further development especially those of a sporo- 
phytic character lie in this region of the protoplasm. They 
must be sought in the nuclei and in the only stable elements of 
the nuclei, the chromosomes. 
It has been held at times by botanists, following the lead of 
certain zoölogists, that the sperm or sperm nucleus introduced a 
centrosome into the egg which organized the first cleavage- 
spindle and thereby played a necessary part in starting cell 
division. Such a centrosome would naturally be sought in the 
