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THE AMERICAN NATURALIST 



[Vol. XLV 



extremely important relation in the study of the geno- 

 types, as will he shown later. 



The second phenomenon which quickly made itself 

 manifest, was first clearly appreciated in the second gen- 

 eration after the beginning of the experiments ; this was 

 the fact that each self-fertilized family possessed mor- 

 phological features which clearly differentiated it from 

 all other families. In most cases the distinguishing 

 characteristics of these families were of such elusive 

 nature that it was impossible to recognize definite unit- 

 characters, and indeed, morphological descriptions of the 

 several pedigrees could often be made only in terms of 

 greater or less intensity of the several qualities ex- 

 hibited. However, the distinctions were real and applied 

 to every member of the particular family. Thus one 

 family might have a very slender, poorly developed male 

 panicle, while another would have more thick and dense 

 branches of the panicle. This difference might be quite 

 small when given in actual measurement but inspection 

 showed that every individual of the one family had the 

 slender, illy developed panicles, while all of the offspring 

 of the other family had the thicker, denser type. Simi- 

 larlv, one family might have « slightly broader and 

 darker green leaf than another, and these characteristic 

 differences were likewise uniformly present in all mem- 

 bers of the single families contrasted. No such character 

 as this is capable of being traced through the generations 

 following a cross, in the manner usually pursued by the 

 geneticist, and the matter must be approached by in- 

 direct methods. The important point to be kept in mind 

 here is simply that the self -fertilized families, derived 

 originally from a common stock, do differ by morpho- 

 logical characteristics, and that there comes to be great 

 uniformity in regard to the presence of these character- 

 istics in all the individuals of a given self-fertilized 

 family. 



This relative uniformity, which is so obvious even to 

 the casual observer, is not sufficient in itself, however, 



