Lawrence's and Brewster's Warblers and Mendelian Inheritance. — In 



any discussion of the status of Lawrence's and Brewster's Warblers it is 

 well to bear in mind that the facts, including the much greater abundance 

 of Brewster's, are in accord with Mendel's Law of Heredity, supposing 

 both forms to be hybrids between Helminihophila pinus and H. chrysoptera. 

 I have written out an hypothetical explanation of the case along these 

 lines, signalizing the two most prominent varying characters of the birds, 

 namely, color of underparts and presence or absence of black throat patch. 

 Familiarity with Mendel's Law is taken for granted, and I would refer 

 anyone to whom it is not familiar to an excellent article on the subject 

 by W. E. Castle in Volume XXXVIII of the Proceedings of the American 

 Academy of Arts and Sciences, January, 1903. 



Let W stand for "white below"; w stand for " absence of white, " i. e., 

 "yellow." 



Let P stand for "plain throat"; p stand for "absence of plainness," 

 i. e., "black throat." 



Then H. chrysoptera is pW; H. pinus is Pw; PW (the pure dominant) 

 is Brewster's Warbler; pw (the pure recessive) is Lawrence's Warbler. 

 H. chrysoptera X H. pinus is pWPw, but in plumage PW, Brewster's 

 Warbler. All the first generation hybrids will be Brewster's Warbler in 

 plumage. In the next generation there will be pure Golden-winged 

 Warblers, pure Blue-winged Warblers, pure Brewster's Warblers, and 

 pure Lawrence's Warblers; also mixed birds of the first three forms, but 

 none of the last form, which, being recessive, comes to light only when 

 pure. - The original hybrids then (which will be all Brewster's in plumage) 

 must be fertile with one another or with the parent species for any Law- 

 rence's to occur; and if they are perfectly fertile Lawrence's must still 

 remain a small minority. After the first generation the proportion of 

 plumages of birds with mixed parentage should be; 9 Brewster's, 3 chry- 

 soptera, 3 pinus, 1 Lawrence's. See Table. 



In plumage 

 PWPW Brewster's 

 pwpw Lawrence's 

 PwPw pinus 

 pWpW chrysopters 



In plumage 

 PWPw Brewster's 

 PWpW 

 PwPW 

 pWPW 



Pwpw 

 pWpw 

 pwPw 

 pwpW 



pmus 



chrysoptera 

 pinus 



chrysoptera 



PWpw 

 pWPw 

 pwPW 

 PwpW 



Brewster's 



9 Brewster's, 3 chrysoptera, 3 pinus, 1 Lawrence's. — John Trbadwbll 

 Nichols, New York City. . 



iHdC 26. Jaa 1908.P. g^6, 



