PRESIDENT’S ADDRESS. 19 
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 
make-up 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 powers normally sup- 
pressed. 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 multi- 
plicity of quills to the tail of the fantail 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 determinations 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 
cross-bred which makes it tall. The pure tall parent had two doses of 
this factor ; the dwarf had none; and since the cross-bred 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 cross- 
ing 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 homozygous— 
formed from similar germ-cells, and that one dose is insufficient 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 perceive that the 
amount of the effect is our only criterion in distinguishing 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. Professor 
Cockerell lately found among thousands of yellow sunflowers one 
which was partly rel. By breeding he raised from this a form wholly 
red. Hvidently the yellow and the wholly red are the pure forms, and 
the partially red is che 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 positive characteristic, and invert the expressions, 
representing the red as RR, the partly red as Rr, and the yellow as 
rr. According as we adopt the one or the other system of expression 
we shall interpret the evolutionary change as one of loss or as one of 
c 2 
