16 PRESIDENT’S ADDRESS. 
variety, ‘Coral King,’ we might claim this as a genuine example of 
variation by loss. The new variety is a simple recessive. It differs 
from ‘ Crimson King’ only in one respect, the loss of a single colour- 
factor, and, of course, bred true from its origin. To account for the 
appearance of such a new form by any process of crossing is exceedingly 
difficult. From the nature of the case there can have been no cross 
since ‘ Crimson King’ was established, and hence the salmon must 
have been concealed as a recessive from the first origin of that variety, 
even when it was represented by very few individuals, probably only by 
a single one. Surely, if any of these had been heterozygous for salmon 
this recessive could hardly have failed to appear during the process of 
self-fertilisation by which the stock would be multiplied, even though 
that selfing may not have been strictly carried out. Examples like this 
seem to me practically conclusive.* They can be challenged, but not, 
I think, successfully. Then again in regard to those variations in 
number and division of parts which we call meristic, the reference of 
these to original cross-breeding is surely barred by the circumstances in 
which they often occur. There remain also the rare examples men- 
tioned already in which a single wild origin may with much confidence 
be assumed. In spite of repeated trials, no one has yet succeeded in 
crossing the Sweet Pea with any other leguminous species. We know 
that early in its cultivated history it produced at least two marked 
varieties which I can only conceive of as spontaneously arising, though, 
no doubt, the profusion of forms we now have was made by the crossing 
of those original varieties. I mention the Sweet Pea thus prominently 
for another reason, that it introduces us to another though subsidiary 
form of variation, which may be described as a fractionation of factors. 
Some of my Mendelian colleagues have spoken of genetic factors as 
permanent and indestructible. Relative permanence in a sense they 
have, for they commonly come out unchanged after segregation. But 
I am satisfied that they may occasionally undergo a quantitative dis: 
integration, with the consequence that varieties are produced inter- 
mediate between the integral varieties from which they were derived. 
These disintegrated conditions I have spoken of as subtraction—or 
reduction—stages. For example, the Picotee Sweet Pea, with its 
purple edges, can surely be nothing but a condition produced by the 
factor which ordinarily makes the fully purple flower, quantitatively 
diminished. The pied animal, suchas the Dutch rabbit, must similarly 
be regarded as the result of partial defect of the chromogen from which 
the pigment is formed, or conceivably of the factor which effects its 
oxidation. On such lines I think we may with great confidence 
* The numerous and most interesting ‘mutations’ recorded by Professor 
T. H. Morgan and his colleagues in the fly, Drosophila, may also be cited as 
unexceptionable cases. 
