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THE AMERICAN NATURALIST [Vol. XL V 



sorts of variations can be distinguished, namely those 

 (a) that are represented in the germinal material and 

 are inherited without substantial modification, as in 

 "pure lines," and those (b) that are somatic and are 

 not inherited. By anything short of the actual breeding 

 test it is quite impossible to tell whether a particular 

 variation observed in the soma belongs to the one cate- 

 gory or to the other. As I have tried to emphasize in 

 other places, it is both to be expected on this view of in- 

 heritance, and is also the case in actual fact, that the 

 somatic manifestation or condition of any character is a 

 most uncertain and unreliable criterion of the behavior 

 of that character in breeding. Finally under the geno- 

 type concept, of course, the whole array of facts brought 

 out by Mendelian experiments find their place. 



Now while certain adumbrations of the genotype con- 

 cept have long been current in biological speculations in 

 regard to heredity, this general view-point owes its 

 grounding in solid facts primarily to Johannsen's work 

 with beans and with barley. It is to be noted that in 

 these cases, as well as in most of the investigations of 

 the pure line theory which have followed Johannsen's 

 work, the organisms used have been such as reproduced 

 either by self-fertilization, or by fission, or by some veg- 

 etative process. This brings us to the consideration of a 

 question of great importance, both theoretical and prac- 

 tical. In cases of dioecious organisms, where a "pure ,r 

 pedigree line in the sense that such lines are found in 

 beans or in Paramecium by definition can not exist, has 

 the genotype concept any bearing or significance? In a 

 general way it obviously has. Probably no one (except 

 possibly some of the ultra-statistical school) could be 

 found who would deny that in general a distinction is to 

 be made between variations having a gametic and those 

 having merely a somatic basis. But specifically how far 

 has the genotype concept any application in case of 

 1 1 non-self ed" organisms? Johannsen in his " Ele- 

 ment e" has thoroughly analyzed Galton's material and 



