No. 463-] STUDIES ON PLANT CELL.— VI. 46 1 



from both gametes maintain their independence and never fuse 

 at the immediate time of fertihzation. We have reason to 

 assume, chiefly from zoological 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 ^gg 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 zoologists, 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 



