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THE AMERICAN NATURALIST [Vol. XLV 



The genotype-differences are nevertheless constant; 

 the "Beaktionsnorms" of the organisms in Woltereck's 

 cases, as well as in the examples just cited, are of course 

 eo ipso 1 1 constantly different ' ' just as well as the ' ' Eeak- 

 tionsnorms" of different chemical compounds. And as 

 to chemical analogies it may perhaps be useful to state 

 that different chemical compounds (the structural or 

 constitutional differences of which surely are granted to 

 be discontinuous and constant) may sometimes show 

 "reaction-curves" highly resembling Woltereck's "phen- 

 otype-curves." It is, I suppose, quite sufficient to point 

 out the temperature-curves of solubility for different 

 salts of sodium and other metals. These curves inter- 

 fere in different ways, cutting each other or partially 

 confluent, in analogy with Woltereck's phenotype-curves. 



The essential point in the whole matter is, of course, 

 that a special genotypieal constitution always reacts in 

 the same manner under identical conditions — as all 

 chemical or physical structures must do. Differences in 

 genotypieal constitution (as well as differences in chem- 

 ical or physical nature) are not bound to manifest them- 

 selves at all — and still less to do so in the same sense 

 — under all conditions. Sometimes even quite special 

 conditions may be required for the realization of possi- 

 bilities ("Potenzen," as some German authors are say- 

 ing), due to a special genotypieal nature: This is a well- 

 known fact in physiology as in the fine art of gardening. 

 Baur has long since emphasized the importance of this 

 point for the Mendelian researches. 



So the criticisms of Woltereck as to the genotypieal 

 discontinuity and constancy are only based upon a re- 

 grettable misconception of the genotype-notion. Over 

 and over we find in current literature this confusion of 

 genotypes with phenotypes, and we even have met with 

 the idea, that the Daphnias of a lake may in summer 

 diverge in different races or varieties, but that in winter 

 they converge into one single race ! In this statement of 

 Wesenberg Lund, the author regards of course only the 

 phenotypes in a purely descriptive manner. It is evident 



