No. 551] 



THE MENDELIAN NOTATION 



037 



is impaired and this is the only excuse for its existence. 

 Furthermore, while it has not been proved that the phe- 

 nomenon we call segregation occurs at the reduction 

 division, the presumption is in favor of that view. The 

 work of Webber, Correns, Lock, Emerson and myself on 

 Xenia in maize indicates that segregation does not take 

 place immediately after reduction, while the work of the 

 Marchals on regeneration in mosses indicates that it 

 does not take place before reduction. 



Now to turn to the kinds of variation that may be de- 

 scribed by the Mendelian notation. Owing to its youth, 

 we can all remember how we wondered, as each new case 

 came up, whether Mendelian phraseology would fit. 

 Since qualitative characters were the ones that could be 

 divided into definite categories they were the ones at- 

 tacked. One by one they were analyzed. The phraseol- 

 ogy did fit. Qualitative characters however form a very 

 small proportion of the characters in animals and plants. 

 The numerous characters are the quantitative, the size 

 characters. If Mendel's law is to be worth anything as a 

 generality, therefore, it must describe the inheritance of 

 these characters. 



To some of us Mendel's law from the first seemed 

 destined to be a notation generally useful in describing 

 inheritance in sexual reproduction. This conclusion was 

 indicated by the simple fact that Mendel's law described 

 many cases in both the animal and the vegetable king- 

 dom. It was inconceivable that this should be the re- 

 sult of coincidence. It was therefore still more incon- 

 ceivable that only a small portion of the facts in each 

 kingdom should come under the scope of Mendelism. 



A basis for the inclusion of quantitative characters 

 was obtained when Nilsson-Ehle and the writer showed 

 that certain qualitative characters gave ratios of 15:1, 

 63 : 1, etc., in the F 2 generation, and in other ways be- 

 haved so that they might be described only by assuming 

 more than one independent gametic factor as the germ 

 cell representative of the character, if the orthodox idea 

 of segregation were retained. From these phenomena 



