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THE AMERICAN NATURALIST [Vol. XLIV 



ment! If the nature and development of the sporophyte, 

 from the standpoint of its inherited characteristics, is 

 determined by what is transmitted to it by its parents, 

 how may these parental tendencies operate unless they 

 are intimately associated — unless some mutual relation, 

 or a "Wechselwirkung" of the entities representing 

 these tendencies, is in continuous activity? Further- 

 more, when the fusion nucleus of the fertilized egg in 

 angiosperms divides, the spirem separates by cross 

 segmentation into the '2.c number of chromosomes, x be- 

 ing male and x female. These sporophytic chromosomes 

 are arranged in lineal series, or end to end, to make the 

 spirem, which splits longitudinally. I do not believe 

 many cytologists will contend that the sporophytic 

 spirem is formed by the lateral coming together of male 

 and female spirems. If the parental chromosomes are 

 arranged tandem to form the sporophytic spirem, why 

 should they be arranged in any other manner to form 

 the heterotypic spirem? 



Returning now to the fecundated egg, it is seen that 

 the fusion nucleus presents the same visible structure 

 as that of either gamete, with the exception that an addi- 

 tional nucleolus or nucleoli may sometimes be observed. 

 The essential demonstrable act in this fusion concerns 

 the nuclei; the behavior of the cytoplasm that may ac- 

 company the sperm nucleus is largely a matter of con- 

 jecture, for it is not possible to trace its behavior with 

 any degree of accuracy, either in the living state, or by 

 means of the indirect method of study. However, to 

 satisfy the demands of the most radical we may admit 

 that sperm cytoplasm unites with egg cytoplasm in the 

 act of fecundation. I have described in some detail the 

 structural union of the sexual nuclei ; for in a later para- 

 graph will be discussed the relative significance of 

 nucleus and cytoplasm in sexual reproduction, and as 

 factors in the transmission of hereditary characters. 



One male nucleus of the pollen-tube is concerned in 

 sexual reproduction as that term is understood in this 

 paper, but as the union of the second male nucleus with 



