Studies on variation and selection. 147 



Thus, for instance, is the difference between two plants, one of 

 which lacks a factor necessary for anthocyan-formation, much more 

 striking, than that between two, which both have this colouring sub- 

 stance, but of which one lacks a gene which in the other changes 

 the colour a little. There are instances such as these, which have 

 given rise to the terms "dominant" and "recessive characters" and 

 to "unit-characters". 



A pair of unit-characters may thus be contrasted, one proper to 

 the organism in whose zygote a gene was present, the other to that 

 from whose z3'gote it was absent. The term "unit-difference" has 

 also been offered, and this has a manifest advantage, for the word 

 "unit-characters" leads one to think of "a unit-character" and to 

 write e. g. "hoodedness in rats is a unit-character" which means 

 nothing whatever. 



It has become more and more evident, that, though such "unit- 

 character-genes" have been the ones most studied, because they are 

 easiest studied, they are by no means the rule. We know genetic 

 factors which influence several apparently unrelated organs, which, 

 for instance, are at the same time indispensable for the development 

 of hair on the stem and of pigment in the flower. Also, there have 

 been found many instances of genes which do not at all influence 

 the development of the organism in which they find themselves, or 

 which, by their presence or absence cause a difference, which is much 

 smaller, than that caused by many non-genetic developmental factors. 

 Thus, we must clearly give up all hope to analyze "an organisms 

 characters into the units". 



These units, to conclude, are incidental things, and not at all 

 fundamental. It is therefore, that we propose to discontinue the use 

 of the term unit-character. 



One of the things which struck Mendel, was that, on crossing 

 two forms, of which one showed a certain character, and the other 

 a different one, it happened that the hybrids in this respect were 

 identical with one parent. This character he called the dominant 

 one of the pair, and that, which disappeared in the hybrid, to 

 reappear in some of the offspring in the second generation he called 

 the recessive character. In fact, all the pairs of characters in the 

 pea, studied by him, behaved in this way. Later, the hypothesis 

 has been made, that in such cases, the organism showed the dominant 

 or the recessive character, because in the first case, a genetic factor 

 cooperated to the development, which same factor was absent from 



