134 BOTANICAL GAZETTE [august 



were derived. They may represent the results of progressive 

 mutations, but here again caution is necessary because of the 

 alternative hypothesis. 



There is also an inhibitor which affects the body of the petals 

 in the "Shirley" poppies, producing what is essentially a dominant 

 white, though the inhibition is often very imperfect, in which case 

 the flowers are more or less washed and striated with color, though 

 generally whitish. 



This supposed inhibitor was evident only in crosses involving 

 at least one red -flowered or striated parent. The same white- 

 flowered plant which was a dominant white in crosses with red- 

 flowered and striated plants was a recessive white in crosses with 

 pink-flowered and red-orange-flowered plants. 



In several cases red-flowered plants crossed together produced 

 a whitish progeny and a similar result was produced when two 

 striated plants were mated or when striated was crossed with red. 



Two hypotheses to account for these facts are considered: 

 (a) that there is one inhibitor affecting only the pure spectrum-red 

 and having no effect on pink and red-orange; the minus-fluctua- 

 tions of this inhibitor pass the limit of visibility; (b) that there are 

 two factors, A and B, which have no visible effect when existing 

 alone, but which act as an inhibitor when brought together. These 

 two hypotheses must be tested by further breeding. 



I take pleasure in acknowledging here the faithful work of 

 Mr. E. E. Barker, who assisted me in making the records upon 

 which this paper is based. 



Station for Experimental Evolution 



Cold Spring Harbor, L.I. 



LITERATURE CITED 



W 



Press. 1909. 



Cambridge: University 



2. Castle, W. E., Heredity in relation to evolution and animal breeding. 

 New York: D. Apple ton & Co. 191 1. 



3. Correns, C, Vererbungsversuche mit blass(gelb)grunen und bunt- 



annua. 



Mirabilis Jalapa, Urtica piliilifera, und 

 Abst. Vererb. 1:291-329. figs, 2. 1909. 



