Races of Paramecium. 547 



8. Diverse, closely related races in other organisms 



It is well known that in more complex organisms belonging 

 to a single species many races exist, differing very slightly in 

 hereditary characters. The extensive work upon this matter 

 has come to be known as "pure line" work, following the example 

 of Johannsen ('03), who showed that many slightly differing 

 "pure lines" exist in beans and barley when self fertilized. The 

 work of de Vries, Nilssen, Shull, East, and many others, have 

 shown the existence in higher plants of many diverse strains, dif- 

 fering slightly bat permanently in hereditary characters. Johann- 

 sen ('09) has recently proposed as a designation for such diverse 

 races or strains the word genotype, and this usage has been 

 followed by others. Mr. T. D. A. Cockerell has called my at- 

 tention to the fact that the word genotype is already in use with 

 another signification, namely, that of designating "any typical 

 material of the type species of a genus." It may be necessary 

 therefore to replace Johannsen's term genotype by some other, 

 as a name for the diverse strains of which a species is formed. 



The question of the existence of diverse permanently differ- 

 entiated strains among lower animals is one of much interest 

 from many points of view, and it has yet been comparatively 

 little studied. The existence of many diverse forms grouped 

 under a single specific name is well known, particularly in plankton 

 organisms, where this has been the object of a recent monumen- 

 tal work by Wesenberg-Lund ('08). This author shows the exist- 

 ence of great numbers of diverse forms of Algae, Protozoa, Crus- 

 tacea, Rotifers, etc., at different seasons of the year or in different 

 localities — each "species" including many such forms. But 

 these are commonly spoken of as ''seasonal variations" and "local 

 variations," and there is a tendency toward the view that these 

 are all modifications due to environmental conditions of what 

 is essentially a single but very plastic stock. According to this 

 view, the same "pure line" would take on one or another of these 

 forms, depending on the conditions under which it existed. The 

 usual opinion is well put by Wesenberg-Lund as follows: "It 

 is only since '95 that the view has become more and more general. 



