BY THE SELECTION OF SOMATIC VARIATIONS. 9 



Although there is this irregular expression of solid-red, variegated, 

 and non-red kernels on the same plant and among different plants of 

 the same generation, and although selection from solid-red tends to 

 give greater numbers of solid-red progeny, Emerson concludes that the 

 factors for solid-red and variegation are "as distinct in inheritance as 

 any two factors could well be" (p. 33). He points out, however, that 

 the "factors" concerned are pattern factors, one determining self- 

 color and the other giving variegation. When a solid-red kernel occurs 

 in an ear of the variegated race, Emerson assumes that a V factor 

 changes to S; but when these red kernels do not give solid-red progeny, 

 he further assumes that in these diploid cells one of the pair of V factors 

 changes to S and that such somatic changes may affect an area of cells 

 including macrospores. 



Taking this at its full value, we note that as the occurrence of solid- 

 red kernels is frequent the hereditary factor V is fluctuating and 

 extremely labile, changing to S readily. For V and S to be distinct in 

 inheritance under such conditions is hardly conceivable, for they are 

 not even distinct in cell lineage. Emerson thus reflects the strong ten- 

 dency of most modern Mendelian investigators to regard their assumed 

 factors as temporary conditions with quite fluctuating activities. 



Such conflicting results as the above, obtained even by careful 

 pedigree methods of study, may well lead one to question whether our 

 knowledge of the behavior of plant characters in inheritance and 

 expression has advanced much beyond the views of Darwin. 



Such studies may well establish the general breeding values of 

 certain characters in particular cases which are of practical significance. 

 The more refined methods of pedigree have shown that plants with 

 identical appearances may give quite different progeny, and that 

 selection for relative degrees of constancy should be made in pedigreed 

 lines rather than in mass selection. Mendelian results also indicate 

 the possibilities of hybridization followed by selection in pedigreed 

 lines of hrybrid progeny. 



In its theoretical significance, however, Mendel's original work has 

 two points of special interest. First, it embodied the conception that 

 all structures of like character are due to a single hereditary unit; for 

 a specific example, all the wrinkles of all the peas on a plant were con- 

 ceived as represented in the germ-cells by a single unit. This was in 

 decided contrast to Weismann's general view that each wrinkle is 

 represented in the germ-cells. The second point of special interest 

 pertains to the behavior of these assumed units in the formation of 

 reproductive cells and their behavior in fertilization. Mendel assumed 

 that they segregated as units independent in behavior and pure in 

 composition from the unit representing the contrasting character. By 

 the conception of the purity of the segregations of hereditary units, each 

 representing only an entire and complete quality or character, Mendel- 



