43 



regard to visible characters, is no longer regarded justifiable, but instead 

 extreme caution is observed lest unsuspected values be overlooked or lightly 

 cast aside. 



IV. THE COMPOSITION OF A RACE OF CEREALS AND ITS 



VARIABILITY 



From the evidence adduced thus far it seems clear that at least some 

 of our common cultivated varieties contain a larger or smaller number of Biotypes 

 distinct hereditary types which, on being propagated separately, breed true, and Element- 

 Johannsen, as already indicated, has given to these entities the name Bio- wy species, 

 types, the progeny of which he calls a "pure line." Such bio-types, together 

 with other intra-specific forms, are commonly spoken of by DeVries, as 

 "elementary species." In self -fertilizing plants such as wheat, oats and 

 barley, pure lines may correctly be called strains, although this term is not 

 always restricted to absolutely pure sorts. In this paper strain will be used 

 to indicate pure lines only. 



The presence of different types within a variety was formerly regarded 

 as a manifestation of some inherent (hereditary) variation, a phenomenon 

 which was believed to be continuous. Experience in the separate culture 

 of these types, however, has shown them to be constant and distinct entities 

 representing probably the smallest systematic division into which plant life 

 can be divided. 



One of the most composite varieties of agricultural plants investigated ,, ,..,. 

 thus far at Svalof is the variety of white oats commonly grown in the Baltic O fp ro bstier 

 region and known under different names of which Probstier is the most oats. 

 common. 



In commenting upon the mixed character of this variety, Nilsson-Ehle 

 (42, p. 125) says: " The multiplicity of forms found within this old unselected 

 race is so great that it is difficult to obtain two individuals which will give 

 identical progeny." The respective progeny of these forms were distinguished 

 by differences in degree of awn-development, hairiness of callus, size, form and 

 color of kernels, average height of straw, width of leaf, etc. 



The fact that two apparently identical plants in an old race may, when inability to 

 cultivated separately, prove to be quite distinct bio-types each producing its distinguish 

 own peculiar progeny, served to show the need of submitting old varieties al1 biotypes 

 to an actual biological analysis. This analysis it was seen, could not be on ihe basis 



restricted to forms which simply appeared different, but must rather embrace 



r J ^ r . appearance. 



a large number of individuals without special regard as to whether these 

 differed in outward appearance or not. 



This is the principle which has been followed by the above author in 

 connection with the extensive analysis to which he has subjected the old 

 Probstier variety during the past ten years. The results of one of 

 these lines of studies may here be given: In 1906 there were sown out 72 

 small plots, each with seed from a single plant taken at random from a 



