348 



THE AMERICAN NATURALIST 



[Vol. XLV 



We recognize three essential propositions: 

 Proposition 1. — Most species or varieties are not 



homogeneous, but are composed of a large number of 



minor forms. 



The series of individuals classified as the same 

 variety or race by the systematist, regarded as homo- 

 geneous material for experiment by the physiologist, 

 lumped together to form a single 11 population" by the 

 statistician, is designated by Johannsen as a phaenotype. 

 This phaenotype may generally be analyzed by pure line 

 breeding into many constant and indivisible strains 

 known as genotypes. 



Systematists have long regarded certain groups as 

 polymorphic. Aster, Rubus, Salix and Cratcpgus at once 

 occur to the botanist and Unio,8almo and the staphylinids 

 to the zoologist. But the genotype theory seems to regard 

 systematic polymorphism as a much wider phenomenon. 

 Indeed one is sometimes assured that every apparently 

 uniform cultivated variety is a swarm of constant bio- 

 types. Johannsen emphasizes the generality of hetero- 

 geneity. For instance, he says: 3 



Kin <re<_r<'beiier Pliacimi vpu- ma^- AusdnwU cincr i > i . > ! o-i s< •] i t-n Kiulii'it 

 es wohl in den allemeisten Fallen nicht f* 



Again on page 162 : 



In der Praxis wirkt ein Selektion meistens schnell in der beabsichtigen 

 Bichtung— eben weil die Bestiinde oder Populationen fast immer 

 Gemische sind. 



One more illustration will suffice: 



Verteilung beweist gar nichts in Being auf Einheitlichkeit des derart in 

 Erscheinung trerenden Typus." Professor Johannsen is apparently un- 

 aware that this point has been fully recogni2ed by "Biometriker " for years. 



