152 MAINE AGRICULTURAL EXPERIMENT STATION. I9II. 



provided only that they conform to purely statistical canons of 

 homogeneity. This assumption of equal hereditary significance 

 for all variations is tacitly made in deducing the law of ancestral 

 inheritance, when individuals are lumped together in a gross 

 correlation table.* The genotype concept, on the other hand, 

 takes as a fundamental postulate, firmly grounded on the basis 

 of breeding experience, that two sorts of variations can be dis- 

 tinguished, namely those (a) that are represented in the germi- 

 nal 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 category or to the other. As I 

 have tried to emphasize in other places, it is both to be expected 

 on this view of inheritance, 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 genotype concept, of 

 course, the whole array of facts brought out by Mendelian ex- 

 periments find their place. 



Now while certain adumbrations of the genotype concept 

 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 bar- 

 ley. 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 repro- 

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

 etative process. This brings us to the consideration of a ques- 

 tion of great importance, both theoretical and practical. In 

 cases of dioecious organisms, where a "pure" 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 bear- 

 ing or significance? In a general way it obviously has. Prob- 

 ably 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 hav- 



* For a more detailed discussion of this point see a paper by the pres- 

 ent writer entitled "Biometric Ideas and Methods in Biology; their Sig- 

 nificance and Limitations," in the Revista di Scienca (in press). 



