Progressive, Retrogressive, Degressive Mutations. 575 
ous or syncotylous individuals. The seeds, however, of 
both types give the same proportion of tricotyls or syn- 
cotvls even when self-fertilization has been insured. 
> 
If we wish to elaborate terminologies still further, 
the term semi-latent may be limited to the anomalous 
character of the half race, and the character of the middle 
race may be described as semi-active (see p. 21). \Ye 
can then distinguish four conditions of one and the same 
factor; the active, the latent, the 
semi-active and the semi-latent. 
This classification may suffice for 
the time ; and at any rate it can 
be said that it is in accord, so far 
as my experience goes, with the 
facts known at present. 
Such a factor cannot be trans- 
ferred at will from one of these 
conditions to the other, either 
by selection or by any other 
means, at any rate in the present 
state of our knowledge. Such a 
transition is only effected by com- 
binations of causes of which we 
still know nothing, or as we say 
by chance. Moreover the tran- 
sitions, so far as we can observe them, are not slow or 
gradual, but take place suddenly. The new race appears 
on the scene at once and unexpectedly, as in the case of 
the peloric Linaria. Sudden transitions of this kind are 
exactly what we call mutations ; and to distinguish them 
from the progressive and retrogressive types, we may 
refer to them as degressive mutations. 
Every mutation therefore consists fundamentally in 
Fig. 135. Papaver com- 
uintatmn polycephalum. 
The same anomaly which 
occurs in P. somnifcruui 
as a middle race (Vol. I, 
Fig. 27, p. 138) occurs 
here as a half race, mani- 
festing the character very 
rarely and only to a small 
extent. 
