BREWSTER'S WARBLER. 73 



P w (pinus) X p W (chrysoptera) 



1 

 Fi P w p W 



That is, the offspring of the first generation will all be impure dominants, 

 but in plumage P W, leucobronchialis. If two of these hybrids of the first gener- 

 ation should mate together and produce offspring the second filial generation 

 would comprise Brewster's Warblers, Blue-wings, and Golden-wings, and also 

 the pure recessive, Lawrence's Warbler (pwpw), in the relative numerical 

 proportion of 9, 3, 3, 1. But we have seen that as far as observations show, 

 Brewster's Warbler always breeds back with one of the hypothetical parent 

 forms, pinus and chrysoptera. In that case the advent of Lawrence's Warbler 

 will be deferred to the third filial generation when it will come to light in small 

 numbers as compared with the dominant hybrid, Brewster's Warbler. 



PwXpW 



pW X PwpW X Pw 



I 1 



chryso. =pWpW Pw Pw =pimis 



leuco. =pWPw PwpW = leuco. 



F2 leuco. =pWPW . iPwPW =leuco. 



chryso. =pWpw -■ •'Pwpw = pinus 



leuco. = pW Pw X pW pw = chryso. 



