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THE AMERICAN NATURALIST [Vol. XL VIII 



F x plant when taken by itself gave some ears as low as 13.7 per 

 cent, waxy, while others exceeded the expected proportions and 

 gave ears as high as 33.3 per cent. waxy. The investigators point 

 out that this variation is not the result of the laws of chance as 

 the deviation is far greater in many cases than the probable error. 

 Therefore, says Swingle, 



there can be no doubt but that their varying percentages represented 

 real differences in the hereditary composition of the first generation 

 plants. It would be hard to find a more conclusive case since there could 

 be no doubt as to the purity of the parents and what is more rare no 

 possible doubt as to whether a given kernel had a waxy or a homy 



Mendelians are said to be unaware how fatal this phenomena is 

 to some of the chief tenets of modern theories of heredity, and 

 they are also accused, somewhat unjustly, I believe, of applying 

 the term "imperfect dominance" to this and to the Citrus 



In this case, both parents were undoubtedly homozygous for 

 their respective endosperm characters, so that heterozygosity will 

 not account satisfactorily for the deviations. But this is a dif- 

 ferent phenomena than Swingle found in his Citrus hybrids, for 

 here one is dealing with a fluctuation in a proportion or ratio 

 involving the same character, while in his experiments the diffi- 

 culty was the variation in presence and absence of distinct and 

 often new characters, indicating an extremely heterozygous 

 parentage. 



As an explanation or working hypothesis for his own and 

 similar data, Swingle advances a somewhat new and suggestive 

 chromosome theory on the assumption that it fills an urgent need. 

 The theory of zygotaxis, as it is called, may be summarized as 

 follows : 



Maternal and paternal chromosomes probably persist side by 

 side in the cells, unchanged in quality and number throughout 

 the whole development of the F, organism. This being true, 

 Swingle, in order to explain his data, assumes that the influence 

 in character formation exerted by chromosomes on the P, hybrids, 

 is in some cases due to their relative positions in the nucleus, and 

 that these relative positions result from accident or at least are 

 determined at the moment of nuclear fusion in fertilization, and 

 remain unchanged in succeeding cell generations. He further 



