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THE AMERICAN NATURALIST [Vol. XLVIII 



of the lobes, those of Treleaseana being sharp, those of 

 the heterozygotic rhomboidca rounded. 



I am fully aware that in thus naming genotypes, I am 

 departing from all rules laid down by systematists. But 

 a rule is useful only as long as it serves a purpose. For 

 the geneticist, the rules of systematists are of small value. 

 Subspecies, variety, form, are, after all, but very general 

 terms, almost incapable of definition because of too fre- 

 quent abuse. But once we have determined the zygotic con- 

 stitution of any plant, we have placed ourselves on a firmer 

 basis. Behavior in breeding is the proper criterion. And 

 while I recognize that this, for systematic purposes, is 

 impracticable, at the same time I assert the right to use 

 a trinomial for any organism of known zygotic constitu- 

 tion, this being, at the present time at least, the easiest 

 way of designating any particular form. Some day we 

 shall have formulas, corresponding to those of chemistry, 

 to designate the lesser forms. 



The increase in the number of named forms, a neces- 

 sary consequence, need cause no a la rm, since they concern 

 only hrm who occupies himself with one species exclu- 

 sively. But we must go even further than this. Squarely 

 facing the issue, we find ourselves placed in a position 

 which necessitates the naming of heterozygotes. Obvi- 

 ously, numerous objections could be urged. But since it 

 has been shown, on the one hand, that certain forms can 

 exist only in a heterozygous form (Barn 's Antirrhinum) 

 and, on the other, that not only the difference between the 

 homozygote and the heterozygote is as great as that be- 

 tween many of our "systematic" species (for instance, 

 attenuata, bbNn, and arachnoid ea, bbNN), but that a 

 homozygotic condition for a single gene gives the same 

 result, whatever the condition of the other known genes, 

 at least as thus far determined (arachnoids occurs as 

 aaBBNN, aaBbNN and aabbXX), the advantage of nam- 

 ing all forms of different zygotic constitution must be 

 granted. 



Thus far we have not encountered a plant of the zygotic 

 constitution BbXX, at least as far as can be judged from 



