22 



In the case of morphological char- 

 acters—at least with the entire series of 

 those whose value in systematic in- 

 vestigations has been generally recog- 

 nized—the distinction between the dif- 

 ferent genotypes is such that the single 

 individual can usually be recognized, 

 in spite of its variations, as belonging' 

 to one or another of the most narrow 

 systematic categories (for example, the 

 "subspecies" of Jordan). 



These morphological types can usu- 

 ally be organized into precise variation 

 series only with great difficulty, for a 

 mixture of individuals of different 

 genotypes might be combined with a 

 series of individuals which belong to 

 a unique genotype. A mixture such as 

 the Oenothera forms of de Vries or 

 Raunkiaer's Taraxacum "Geschlech- 

 ter" ^ gives with regard to the essential 

 morphological characteristics a differ- 

 ent picture than a pure culture of a 

 single form. 



With regard to all sorts of char- 

 acters of a more physiological sort— 

 the non-botanical characters of Hj. 

 Nilssons— such as, for example, most 

 height and other proportions, bio- 

 chemical properties, reliable numerical 

 relationships, and others, we have a 

 different situation. The distinct, ac- 

 tually existant genotypes, easily dem- 

 onstrated through isolated cultivation, 

 show only quantitative differences, so 

 that the variation curves of the differ- 

 ent genotypes overlap, and one has the 

 transgressive curves of Hugo de Vries. 

 A mixture of individuals, which belong 

 to genotypes clearly distinct with re- 

 spect to one of these characteristics 

 (compare small and large, as well as 

 narrow and broad beans) can very 

 easily form so continuous a variation 

 series that it is not possible to recognize 



1 Raunkiaer, C, "Kinidannelse uden Be- 

 frugtning hos Maelkebotte" {Botan. Tids- 

 skrift, Bd. XXV, Kopenhagen, 1903), pp. 

 109-119. 



JOHANNSEN 



directly the distinctions between geno- 

 types, and the average value will be 

 erroneously regarded as that of a single 

 genotype. In cases such as these it is 

 impossible to distinguish the genotype 

 to which a single individual belongs. 

 Table 1 is a good illustration of this 

 point. 



It is for these reasons, which have 

 been more or less clearly recognized 

 or just sensed, that the study of the 

 characters I might call "truly" mor- 

 phological, described above, have pro- 

 vided the center of gravity for sys- 

 tematics. The more physiological 

 characters have entered into the sphere 

 of interest of the systematist only in 

 recent years, particularly with regard 

 to lower forms. These reasons also 

 explain why the students of mutation 

 have found the mainstay of their re- 

 searches in true morphological char- 

 acters. On the other hand, these char- 

 acteristics, which essentially determine 

 the entire habitus of the plant, either 

 cannot or can only partially be ex- 

 pressed in numerical measures, and this 

 almost invariably reduces their value 

 to within the limits of the exact 

 methods of measurements and calcula- 

 tion. 



Biometrical research, that is, the in- 

 vestig^ation of the laws of variation and 

 heredity, has thus included primarily 

 the more physiological characters or 

 in j^eneral the characters Bateson 

 called "meristic," that is, those \\hich 

 can be expressed clearly in numbers, 

 such as size or weight. And here, 

 where comparisons of individual with 

 individual does not enable one to dis- 

 tinguish differences in genorv^pe from 

 the manifestations of a fluctuating var- 

 iability, is the stronghold of the Gal- 

 ton-Pearson concept: Here one must— 

 if one fails to consider pure lines— 

 necessarily come to the conclusion that 

 selection of strongly variant individ- 

 uals (either plus or minus variants) 



