No. 526] SEXUAL REPRODUCTION IN GYMNOSPERMS 601 



another, but become so mixed that the male and female 

 chromosomes can not be distinguished. Each chromo- 

 some then splits and during the completion of the mi- 

 tosis twenty-four chromosomes go to each pole to form 

 the first two nuclei of the sporophyte generation. Con- 

 sequently, during this process which we call fertilization, 

 there has been no blending of the chromatin contributed 

 by the two parents. Whether a real blending takes 

 place as the two groups of chromosomes pass from the 

 telophase of the first mitosis into the resting reticula of 

 the daughter nuclei, is still undetermined. Personally, 

 I am inclined to think that there is no blending, either 

 at this early stage or later, but rather, that the chro- 

 matin contributions remain distinct throughout the life 

 history. Whether there is, during the synapsis stage of 

 the reduction division, sufficient fusion to impair the 

 identity of the individual chromosomes, still remains to 

 be demonstrated. 



Although the chromosomes of the two groups become 

 so mixed that they can not be distinguished, the well- 

 known mechanism of mitosis makes it certain that one 

 half of each chromosome contributed by the two parents 

 will reach each of the two daughter nuclei resulting from 

 the first division of the fertilized egg. The same mech- 

 anism of mitosis makes it very probable that this equal 

 representation of the two parents will continue through- 

 out the life history of the plant. 



In all the genera which have been studied, more or less 

 cytoplasm enters the egg with the male nucleus. In the 

 cycads the entire sperm enters the egg and the cilia may 

 continue to move after the sperm is within the cytoplasm 

 of the egg, but the nucleus of the sperm soon slips out 

 from the cytoplasmic sheath and advances toward the 

 egg nucleus, leaving most or all of the cytoplasm in the 

 upper part of the egg. In other forms, like Torreya, 

 Juniperus and Taxodium the cytoplasm of the male cell 

 surrounds the fusion nucleus and takes part in the forma- 

 tion of the embryo, but in most genera, no such cyto- 



