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THE AMERICAN NATURALIST [Vol. XL V 



combinations of the various characteristics of plants and 

 animals "breed true" to those characteristics. Just as 

 the first recognition of permanent differences in pure 

 lines involved easily di>tinguishal>lo characters, so also 

 these first discoveries of permanent pure-breeding geno- 

 types in cross-bred plants and animals involved easily 

 definable morphological characteristics. The demonstra- 

 tion that in normally pure-bred lines there are distinc- 

 tions more minute than such easily visible features as 

 characterize the elementary forms of Draba and many 

 other species, was an important advance in our analysis 

 of the populations which make up the species of plants 

 and animals. A similar demonstration that populations 

 of cross-breeding plants and animals are composed of 

 fundamentally distinct types, intermingled but not 

 changed by panmixia, and capable of being separated by- 

 appropriate means and of being shown to possess the dis- 

 creteness, uniformity and permanence already demon- 

 strated for the genotypes of self-fertilized and clonal 

 races, will add greatly to the importance of the funda- 

 mental conception of permanency of types involved in 

 the work of De Vries and Johannsen. 



For the study of this problem there is probably no 

 better plant than Indian corn. It is known to exist in a 

 large number of obviously distinct strains or subspecies 

 which cross together with the greatest ease. Many of its 

 characteristics have been proved by different investiga- 

 tors to be Mendelian unit-characters ; such, for instance, 

 as the color of the seed-coat, whether red, dark yellow, 

 light yellow, variegated or colorless, the color of the 

 aleurone layer, whether blue, red or white ; the color of 

 the endosperm, whether yellow or white; the chemical 

 composition of the endosperm, whether starchy or sugary, 

 the color of the silks and cobs whether red or white, etc. 

 It has become known also, mainly through the excellent 

 work done at the Illinois State Experiment Station, that 

 oil-content and protein-content of the grains, the posi- 

 tion of the ears, the number of ears on the stalk, and 



