230 Non-Isolable Races. 
choice was largely determined by the fact that there 
were no published records of 4- or 5-foliate leaves of this 
clover, 1 which means that the character, if present in a 
latent state, is much rarer than in the red clover. 
I take this opportunity of calling attention to the 
inestimable value of PENZIG'S "Teratology," This lies per- 
haps rather on the negative than on the positive side, 
for it is of course possible to collect the main literature 
relating to a given question oneself, although not with- 
out the expenditure of a great amount of time; but if 
one is not a teratologist by profession, it seems hardly 
possible without some such help, to satisfy oneself that 
Fig. 45. Tri folium incarnatum, 4-foliate leaves, the middle 
one with incomplete segregation of a lateral leaflet. 
absolutely no records relating to a particular phenomenon 
exist. 
The first step in a purely scientific breeding experi- 
ment evidently is to find out whether the deviation in 
question has occurred before, and if so, whether it is rare 
or common. My belief is that the commoner anomalies 
are heritable characters with a high index of inheritance 
(often about 30-40% or more), but that the rarer ones 
are the occasional expressions of latent or semi-latent 
characters. These are also inherited in their latent state, 
and if they turn up here and there this latent condition 
must probably be widely distributed. 
1 0. PENZIG, Pflanzcnteratologie, Vol. I, 1890, p. 385, where 
incarnatum is not even mentioned. 
T. 
