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THE AMERICAN NATURALIST 



[Vol. XLII 



is incumbent next to determine what this tendency is. There 

 are several possibilities: (1) The germ-cells may have the sex- 

 tendency of the plant from which they came, the egg-cells the 

 female, the sperm-cells the male; (2) they may have the opposite 

 sex-tendency; or (3) some of the eggs may be of one sex-tend- 

 ency and a part of the other, and likewise the sperm. A further 

 problem arises as to how far fertilization plays a role in sex- 

 determination, since thus germ-cells of different sex-tendencies 

 may unite ; and also how far external influences have significance 

 in that they can act upon the sex-tendency of the germ-cells 

 before fertilization, or at the time of fertilization upon the united 

 product, or after fertilization on the embryo. 



"Whether a given germ-cell contains a fixed sex-tendency can 

 best be ascertained when such a cell can be caused to develop 

 without fertilization into a sexually mature individual. Such 

 conditions obtain in cases of "habitual parthenogenesis." The 

 facts here at first sight seem to compel acceptance of the position 

 that the sperm-cells play no role. However, on closer scrutiny 

 of the facts, doubts are raised as to the validity of such an in- 

 terpretation. One must not forget that generally eggs that de- 

 velop parthenogenetically do not undergo a reduction division. 

 Correns states that whatever significance one may attach to re- 

 duction, he can not regard such eggs as of like nature with those 

 that have suffered maturation. In the case of "habitual par- 

 thenogenesis" one deals with phenomena of adaptation. Such 

 adaptation may enable an egg to develop without fertilization 

 even though this capacity depends only on the suspension of a 

 check, which otherwise, through the intervention of a male germ- 

 cell, could exert its influence. In similar manner the sex-tend- 

 ency also may be influenced. Natural and artificial partheno- 

 genesis yield an indication of the sex-tendency only of the egg. 

 "Ephebogenetic" development of sperm-cells, theoretically pos- 

 sible, but practically thus far beset with insuperable difficulties, 

 is urgently required. Merogony furnishes no positive results 

 until we know definitely the role of cytoplasm, as distinct from 

 karyoplasm, in heredity. 



Correns turns into other fields which seem to lead farther 

 than experiments with artificial parthenogenesis, namely, hybrid- 

 ization. The controlling idea of Correns 's investigation is the 

 following: The egg-cells of a dioecious form whose sex-tendency 



