158 PROBLEMS OF GENK 



Pinus Civ 



l. Mantle and lower parts yellow (Y 1 ). I. ' 



a. Wing-bars white (y 1 ). 2. Wing-bars < 



3. Cheek and throat not black (b). 3. Cheek and a 



The grey pigment of the mantle is comm< ut is 



masked by the yellow in pinus, the net result .ve- 



green. 10 



I am much indebted to Dr. F. M. Chapman for the loan of 

 the coloured plate in which these distinctions are shown. It ,. 

 appeared in his book, North American Warblers. 



We cannot tell whether yellow or not-yellow is due to the 

 presence of a factor, but we may suppose that one or other 

 give& the special colour to the parts. The black of character 3 

 is no doubt a dominant. Thus pinus becomes Y J y 2 b and chry- 

 sopiera in y 1 Y 2 B. The Lawrencei which has the underparts 

 yellow, wing-bars white, and black patches is Y x y*B and leuco- 

 fronchialis which has mantle and 



ts 



'.snrio? anibfiisaJm 9#> to aiio i^ 

 T^loVsnibErg-raJni ^fto' fcr 



.ote 

 Wl . O 



view of the case. In vets the dif- 



ficulty which ( ''ronchialis as in 



any sense derived iroiu pin us \s};idi has a yellow breast, and 

 chrysopiera which ha& a b' : leucobronchialis 



has neither. We now re. this form could be 



produced by ordinary re- -jf the absence of Y 1 with 



the absence of B. 



I note also with great interest that the modern observers 

 agree that the so-called hybrids may have the song either of 

 the one species, or of the other, or a song intermediate between 

 the two. It may also be added that these two types have several 



10 It would aid greatly in factorial analysis if the descriptive term "green" 

 could be avoided in application to cases where the green effect is due only to a 

 tiire of black and yellow pigments. The absence of yellow is the sole difference 

 between the mantle and underparts of pinus and chrysoptera. 



