454 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
The differences between varieties or races of chicory are, con- 
sidered as a whole, quite continuous. The averagenumber of flowers 
per head for the first date of bloom (a) (computed from the seasonal 
record of the various members) for the diff traces isolated in Ез 
and F; ranges from 20.4 to 16.7. These averages, however, are from 
distributions that are overlapping (TABLE 48). If the races having 
highest and lowest values of a be massed in population, the curve 
will be bimodal, the irregularity of which depends largely on the 
relative numbers. If the race with intermediate values be also 
massed, then the curve becomes monomodal. 
It is clear that in chicory flower number per head is a character 
that is subject to wide and continuous variability that is (1) par- 
tial (existing among the parts of a single individual and here 
involving also elements of differentiation according to position), 
(2) individual (characteristics of plants as wholes based on their 
entire record), and (3) racial (fluctuating about a mode that can be 
somewhat closely maintained by selection). The differentiation 
between races as such, however, is no more marked than the dif- 
ferentiation involving position that occurs among the various 
parts of the individual. Most especially is the character of num- 
ber of flowers per head subject to modification during ontogenetic 
development and epigenetic processes of growth. Flower number 
per head is very different, therefore, in nature from the general char- 
acter of the inflorescence as a whole and from the character of flowers 
as individuals. All flowers are quite alike, all are in heads, but 
the number of similar flowers that are thus grouped is variable. 
The operation of heredity in such a character as flower number 
is seen in the isolation of races which may be maintained by such 
selection as was possible in chicory. Within each race, however, 
there are further variations, continuous in gradation and.of the 
same nature as those appearing in a more mixed population, which 
are unmistakable evidences of the instability of characters and 
hereditary units. 
BIBLIOGRAPH Y 
Bateson, W. 1901. Heredity, differentiation, and other conceptions 
of biology. Proc. Roy. Soc. t9or. 69: 193-205. 
—— 1903. Variation and differentiation in parts and brethren. 
. Belling, J. 1912. Note in Am. Breeders Mag. 3: 311, 312. 
