158 PROBLEMS OF GENETICS 



Pinus Chrysopiera 



z. Mantle and lower parts yellow (Y 1 ). z. Mantle and lower parts grey (y 1 ). 



a. Wing-bars white (y*). 2. Wing-bars yellow (Y 1 ). 



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



The grey pigment of the mantle is common to both, but is 

 masked by the yellow in pinus, the net result being an olive- 

 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 first 

 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 



gives the special colour to the parts. The black of character 3 



Moubt a dominant. Thus pinus becomes Y l y 2 b and chry- 



The Laivrencei which has, the underparts 



white, and 



.anno* a nH>sis*m srf* to one ;9 i B m -.-wid-i 



i arfi to liftoius ;<A&m ".-wld -r : 77 J 



.01^ 



.g . 



.^osis ana for some 



,d .01*5 



airy correct 



se. In particular we can see how it meets the dif- 

 ficulty which Chapman felt in accepting leucobronchialis as in 

 any sense der which has a yellow breast, and 



chrysoptcr throat, seeing that leucobronchialis 



has neither. We now recognize at once that this form could be 

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

 the absence of B. 



I note also with great interest that the modern observers 



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 



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 mix- 

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

 * en the mantle and underparts of pinus and chrysoptera. 



