150 • TORREYA 



Criterion 11. Direction Indicated by Seasonal Appearance 



Although Adams was aware of this criterion at the time of publication of 

 his first list (1902a), he did not include it until later (1909). In the northern 

 hemisphere, vernal activity suggests boreal origin. He also thought that there 

 is an altitudinal as well as latitudinal relationship, i.e., that mountain forms 

 spreading downward should belong to the vernal aspect, and lowland forms 

 spreading upward should belong to the aestival aspect. 



It is undoubtedly true that such relationships between origin and aspect 

 occur. It does not seem to me, however, that this criterion expresses any inher- 

 ent indication of origin. The described relationship could exist, for example, 

 for a form or series of forms occupying montane, subalpine, and alpine belts 

 (or the corresponding latitudinal zones) with the center of origin in either 

 terminal belt or the middle. The limitations to the spread of a form are found 

 in the action of the whole environment upon the physiolog}- of the form, with 

 such factors as temperature, light intensity, and photoperiod operating. There- 

 fore, it would seem as easy and sound to conceive of a vernal form of the south 

 spreading northward with a change to aestival aspect, as the reverse. This fact 

 seems to me to illustrate perfect!}' the pitfialls of deductive reasoning and gen- 

 eralization. 



Criterion 12. There is an Increase of the Xumber of Dominant Genes 



TOWARDS the CeNTERS OF OrIGIN 



This criterion could only have been proposed after the development of 

 genetics and is appended to the older ones of Adams because of its apparent 

 validity. It can, I think, be attributed solely to \'avilov (1927), who said, "The 

 direct study of the centres of the origin of cultivated plants . . . has revealed not 

 onlv a great diversity of forms but also a prevailing accumulation of dominant 

 forms characterized by dominant genes in the centres. A considerable number 

 of plants investigated show this regularity . . . The secondary centres of the 

 origin of forms are, on the contrary, characterized by a diversity of chiefly re- 

 cessive characters." 



Several cases are discussed by \'avilov, but only one will be mentioned here 

 by wav of illustration. The center of origin of cultivated rye and the genus 

 Sccalc to which it belongs is in Eastern Asia ]\Iinor and Transcaucasia. Here 

 are all the species of rye and the whole diversity of characters of the varieties ; 

 but also here are concentrated the dominant characters of red-eared, brown- 

 eared, black-eared, and marked pubescence of flowering glumes. In the second- 

 ary centers are such recessive characters as liguleless leaves, yellow-ears, and 

 glabrous glumes. Cultivated plant types in their progress from their principal 

 srenetical centers seem to exhibit a "falling out" of the dominant genes and 



