Analysis of Heterogeneity in Complex Characters 255 



As far as the continuity of this group is concerned and their gametic identity 

 of constitution, I am fully agreed with Johannsen and others that they are capa- 

 ble of isolation, are analytical realities, and breed true under constant condi- 

 tions, and further, that they frequently mutate to other biotypes within the gen- 

 eral population. I am not convinced that they are stable, elemental units in the 

 species, as many consider them. They represent more or less stable combi- 

 nations attained in the gametic complex, and are but momentary pauses in the 

 ceaseless metathetic recombinations which each organic group is constantly 

 undergoing. That these biotypes are not capable of modification, or are capable 

 of modification only by sudden change, is true for some, not true for all, and in 

 the next section I shall show how these biotypes can be changed by different 

 agencies. 



THE MODIFICATION OF PWMARY BIOTYPES. 



In the attempt to modify any of these minor groups, be it genotype, clone, or 

 biotype, an hereditary historic influence suggests selection and external condi- 

 tions, and when these have been adequately or inadequately tested, other possi- 

 bilities may then receive attention. Again and again have workers with pure 

 lines, clones, genotypes, or biotypes recorded their inability to produce changes 

 in the types they had isolated. No difficulty is encountered in discovering and 

 isolating races that are alike in most of their characters, but differ in one essential 

 character which sets it off, and when reared in " pure lines " keep it distinct from 

 its fellows. Nevertheless, no effort seems to be able to modify this into another 

 one. 



Jennings, in his masterly studies in Paramoecium, where sexually produced 

 " clones " were used, finds that he was unable to modify or transmute any of his 

 " clones " into another, either new or existing. Johannsen and others in beans, 

 Nillson-Ehle with grains. East, Shull, Emmerson, working with genotypes and 

 biotypes, found difficulty where modification was attempted. Many workers 

 using phenotypes or elementary species, as De Vries, have found difficulty in 

 modifying them. Why this difficulty? Is it real, a limitation upon one's 

 experimental ability, or is it due to lack of skill and understanding? 



The attempt to modify these groups by so-called selective methods seems an 

 indifferent characterization of what one has tried to do, and the word " selec- 

 tion " implies a choice between two or more possibilities rather than a chance 

 determination of what happens. This selective problem is a large one and is one 

 upon which I shall wish to dwell at length later on. I have used, as methods of 

 attempting modification, accumulation of pigment surface in the pronotum as a 

 whole; accentuation of directions of variation in the elements of the pattern 

 (particular spots) ; synthetic combination of directions of variation; external 

 incident climatic forces ; and food and metabolic disturbances. 



EFFECTS OF QUANTITATIVE ACCUMULATION OF PIGMENT. 



Almost all selection investigations degenerate into the effort to accumulate the 

 same quality or attribute by quantitative additions ad infinitum. The odd idea 

 that existing strange modifications of supposed adaptions in nature have arisen 

 by continuous accumulations of minute amounts of the quality lies at the base of 

 this experimental effort. It is notorious that this quantitative accumulation soon 

 reaches a limit beyond which the modification does not extend. This limit in the 



