3 i _i Vierte allgemeine Sitzung. 



tory in 1904 Durham undertook the crucial test of the theory, 

 namely, to determine whether from the differently colored skins 

 of birds and mammals, there could be extracted specific enzymes 

 capable of oxidizing a chromogen — tyrosin — to the specific color 

 of the skin from which the enzyme was taken. That is to say, 

 whether specifically different tyrosinases exist in skins of different 

 color. Only a preliminary report (1904) of these studies has ever 

 been published, but they seem completely to substantiate Cuenot. 

 It is stated that from the black skins of birds and mammals an 

 enzyme can be extracted which is capable of oxidizing tyrosin to 

 black; from yellow skins, an enzyme capable of oxidizing tyrosin 

 to yellow; and from white skins apparently no enzyme capable 

 of oxidizing tyrosin can be extracted. 



If the results so reported were entirely correct and reliable, 

 and if the methods by which they were obtained were quite faultless, 

 I believe that much of the distance would be traversed toward 

 the complete establishment of the 'presence and absence' hypo- 

 thesis, and this in quite perfect accord with the lines laid down 

 by Cuenot. Here was an apparently crucial test which at 

 one stroke seemed to fulfill all of C u e n o t 's prophecies. 



In a paper on the development of the melanin colors published 

 in 1909 I pointed out many facts at variance with C u e n o t 's 

 hypothesis and with Durham 's results. These facts led me there 

 to question both the theory and its conf irmation ; D u r h a m 's 

 paper being criticised on the basis of its own internal, rather 

 than on experimental evidence. At the same time I sketched a 

 number and variety of facts which enabled me there to present 

 a consistent statement of the basis of color development and 

 inheritance. 



Since that time there have been published from the Cam- 

 bridge laboratory, two or three papers by Miss W h e 1 d a 1 e 

 which bear on the subject in hand. In the first of these (1909a) 

 this author reports upon a search for specific chromogens, or 

 absence of chromogens in flowers of specific color, or of no color. 

 I had stated that an organism without chromogen is inconcei- 

 vable ; Wheldale reports that in the plants with which she 

 worked, even in the non-anthocyanic varieties i. e. in their white 

 and cream flowers, was found "a colorless flavone (chromogen)", and 

 concluded "hence, loss of power to produce color in white and 

 cream is (here) not due to loss of chromogen". Wheldale 's 

 (1909b) second paper dealing with A ntirr hinum contains, however, 

 a conclusion (No. 6) at variance with the above. It is there said 

 "complete absence of any chromogen both of the ivory and the 

 yellow from the Zygote results in a true albino bearing pure white 

 flowers and incapable of producing any pigment. The albino 

 however can carry either the oxidase, or the modifying ferment 

 or both." I call attention to the fact that this conclusion, however, 



