374 ANNUAL EEPOET SMITHSONtAN INSTITUTION, l9l5. 



in the wild crab apple. I can not positively assert that this is so, 

 but I think all familiar with Mendelian analysis would agree with 

 me that it is probable and that the wild crab contains presumably 

 inhibiting elements which the cultivated kinds have lost. The legend 

 that the seedlings of cultivated apples become crabs is often repeated. 

 After many inquiries among the raisers of apple seedlings, I have 

 never found an authentic case; once only even an alleged case, and 

 this on inquiry proved to be unfounded. I have confidence that the 

 artistic gifts of mankind will prove to be due not to something 

 added to the makeup of an ordinary man but to the absence of 

 factors which in the normal person inhibit the development of 

 these gifts. They are almost beyond doubt" to be looked upon as 

 releases of powere normally suppressed. The instrument is there, 

 but it is " stopped down." The scents of flowers or fruits, the finely 

 repeated divisions that give its quality to the wool of the Merino or, 

 in an analogous case, the multiplicity of quills to the tail of the fan- 

 tail pigeon are in all probability other examples of such releases. 

 You may ask what guides us in the discrimination of the positive 

 factors and how we can satisfy ourselves that the appearance of a 

 quality is due to loss. It must be conceded that in these determina- 

 tions we have as yet recourse only to the effects of dominance. When 

 the tall pea is crossed with the dwarf, since the offspring is tall we 

 say that the tall parent passed a factor into the crossbred which 

 makes it tall. The pure tall parent had two doses of this factor, the 

 dwarf had none ; and since the crossbred is tall we say that one dose 

 of the dominant tallness is enough to give the full height. The 

 reasoning seems unanswerable. But the commoner result of crossing 

 is the production of a form intermediate between the two pure 

 parental types. In such examples we see clearly enough that the 

 full parental characteristics can only appear when they are homo- 

 zygous — formed from similar germ cells — and that one dose is insuffi- 

 cient to produce either effect fully. When this is so we can never be 

 sure which side is positive and which negative. Since, then, when 

 dominance is incomplete we find ourselves in this difficulty, we per- 

 ceive that the amount of the effect is our only criterion in distinginsh- 

 ing the positive from the negative, and when we return, even to the 

 example of the tall and dwarf peas, the matter is not so certain as 

 it seemed. Prof. Cockerell lately found among thousands of yellow 

 sunflowers one which was partly red. By breeding he raised from 

 this a form wholly red. Evidently the yellow and the wholly red 

 are the pure forms and the partially red is the heterozygote. We 

 may then say that the yellow is YY with two doses of a positive 

 factor which inhibits the development of pigment, the red is yy 

 with no dose of the inhibitor, and the partially red are Yy with only 

 one dose of it. But we might be tempted to think the red was a 



