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THE AMERICAN NATURALIST [Vol. XLIV 



plasm is visible and the embryo is formed from a rather 

 small portion of the basal region of the egg, quite remote 

 from whatever cytoplasm may have entered the egg with 

 the male nucleus. 



On such evidence we could not claim, logically, that 

 cytoplasm does not play an essential part in inheritance, 

 for the egg at its first segmentation contains cytoplasm 

 brought in with the male nucleus, but we believe that 

 the series which we traced in spermatogenesis presages 

 the final elimination of any cytoplasm as a part of the 

 male contribution, and the series could be carried into 

 the angiosperms, where, in some cases, the male contri- 

 butes only a nucleus without any cytoplasm. 



In nearly all the gymnosperms the immediate response 

 to the stimulus of fertilization is a series of nuclear divi- 

 sions which follow each other in such rapid succession 

 that no cell walls are formed between the nuclei. The 

 divisions are simultaneous, probably because the nuclei 

 are in a common mass of cytoplasm exposed to the same 

 conditions. In the large eggs of the cycads, the free 

 nuclear divisions continue until there may be more than 

 a thousand nuclei, but in forms with smaller eggs, the 

 period of free nuclear division is correspondingly re- 

 duced, so that we can select a series of genera which 

 show more than a thousand free nuclei, 256 nuclei, then 

 32, 16, 8, 4 and finally no free nuclear division at all, the 

 first nuclear division of the fertilized egg being followed 

 by the formation of a wall between the daughter nuclei. 



These early stages in the gymnosperm sporophyte are 

 remarkably like the early stages of the garnet ophyte, 

 which also has a prolonged period of free nuclear divi- 

 sion before walls begin to be formed, but the conditions 

 are also very similar. The most striking difference be- 

 tween the sporophyte and gametophyte in these early 

 stages is that during mitosis one shows twice as many 

 chromosomes as the other. Very soon, of course, the 

 two generations become very dissimilar. It is worth 

 recalling, in this connection, that in some algae, like 



