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THE AMERICAN NATURALIST [Vol.XLIV 



cytoplasm. These nuclei contain the haploid number 

 of chromosomes. In the development of the egg, the 

 same number of chromosomes is strictly preserved, no 

 matter what mitotic peculiarities may be observed in any 

 other cells of the embryo-sac, apart from the egg-appa- 

 ratus. The egg differs from the sperm in appearance 

 chiefly in the amount of cytoplasm present, but the cyto- 

 plasm of the one is similar to that of the other. Apart 

 from difference in shape, which is of no importance in 

 phanerogams, the sexual nuclei reveal identical chro- 

 matin structures at the time of union, for both are in the 

 resting, or non-mitotic state. Chromatin granules of 

 the sperm nucleus mingle with those of the egg. When 

 the nuclear membranes between the two contiguous nuclei 

 have disappeared, it is not possible to distinguish pa- 

 ternal from maternal chromatin. It is not seen that 

 chromatin particles of the sperm fuse or become paired 

 with those of the egg nucleus. The gamete nuclei do 

 not remain in any manner separate or distinguishable 

 from each other, as in certain lower plants and in some 

 animals, and one of the very interesting and important 

 problems from the standpoint of hereditary considera- 

 tions is the relation of male and female chromatin, dur- 

 ing the life of the sporophyte. A number of authors 

 have offered explanations of this relation based on ob- 

 servations made upon the first, or heterotypic, mitosis 

 in the spore mother-cells, i. e., at the end of the sporo- 

 phytic cycle. Strasburger ('05) and Gregoire ('05), to- 

 gether with a number of their more recent students, 

 maintain that the maternal and paternal homologous 

 chromatin parts become associated in pairs previous to 

 and during the synaptic balling up of the nuclear con- 

 tents in the first mitosis of the spore mother-cells. This 

 process, they assert, leads to the formation of two 

 spirems (one paternal and- one maternal) which become 

 united side by side, to form the double chromatin thread, 

 in which the homologous parental chromatin parts are 

 brought near to each other. 



The writer (Mottier, '07, '09) does not agree with this 



