70 THE AMERICAN BOTANIST 



ern Maine and planted, the plants would not experience a 

 length of day below 15 hours until about August 1. Therefore, 

 they could not come into flower until after August 1 and, 

 though the vegetative growth might be very rank, they could 

 not mature seed before killing frosts intervened. The long 

 days, therefore, make it impossible for ragweed to perpetu- 

 ate itself in that latitude. On the other hand, plants that get 

 their flowering stimulus from a long day could not perpetuate 

 themselves through seed formation at the equator, where the 

 day never exceeds 12 hours. This principle affords the clue 

 to the fact that many plants grow most luxuriantly near the 

 northern limit of their range. The long northern day allows 

 them to attain their maximum growth before the shorter day 

 intervenes to check vegetative growth and start the produc- 

 tive process. The migration of birds is also said to be ex- 

 plained by this theory. 



Bi^iK Axu YEI.LOW Lupines. — I am sending you two 

 lupines (Zy. arhorcus and L. Clianussonis) which grew near 

 each other on one of the beaches here, as being one of the few 

 exceptions to blue and yellow species in the same genus. Grant 

 Allen suggests that where yellow flowers are found among 

 advanced genera, it means retrogression .and the blossoms are 

 rarely bright yellow, but generally buff' or salmon. This I 

 have found to be the case with the enclosed exception, which 

 could not well be a brighter yellow. How do you account for 

 it? — Mary L. DcLangc, LaJolla, Calif. [There are a good 

 many things about flower color not accounted for as yet be- 

 cause botanists have been more concerned with collecting and 

 naming plants than they have in studying their life processes. 

 Off hand one would be inclined to say that there is no reason 

 why yellow and blue flowers should not be found in the same 

 genus, except that it is not the fashion. There is a funda- 

 mental difference, to be sure, in the methods bv which blue and 



