372 BOTANICAL GAZETTE [NOVEMBER 
tion are to be accounted for in this way. I have already shown that 
my first collection in 1900 was made long after the beginning of the 
flowering season, and hence had the earliest heads with low numbers 
of parts associated with the heads having the highest numbers of parts 
produced during the season, and this fact sufficiently explains the 
high correlations found in that collection. A similar explanation 
may account for the considerable increase in the coefficients of corre- 
lation between the parts of the heads in 1903 as compared with those 
of 1900, as there are associated in the 1903 collection the heads of 
conservative individuals and those of individuals which were much 
modified because of their great sensitiveness to the unfavorable 
conditions in the latter year. It is apparent, therefore, that in cases 
of changed coefficients of correlation, as in other cases, it is necessary 
to scrutinize carefully the influence of more or less artificial conditions 
upon the value of the constants before we can appreciate their biological 
significance 
The results of this study have fully borne out the suggestion that 
considerable differences may occur in individual variation from 
year to year, and it shows that such differences may be even greater 
than one would expect. It is not likely that this is an extreme case 
nor that the differences between these two collections is even near 
the limit for this species. To some these results may seem to Pre 
clude the possibility of deriving anything of further value from quan- 
titative studies of variation, while to others many new problems of 
great interest and importance will be suggested. The interpretations 
which students have based upon the assumption that seasonal flue- 
tuations do not occur will have to be greatly revised or discarded 
altogether, and before we can appreciate the exact bearing of any 
case of variation upon the great problems of evolution it will be nec 
sary to know the laws governing that variation. It is to -_ 
this nature that students must direct their earnest attention pe 
are ever to have a basis for the appreciation of the bearing of in 
vidual variation. 
VI. SUMMARY. 
A second collection of heads of Aster prenanthoides Mubl. wat 
made in 1903 from the same area at Clifton, Ohio, that 
material for a quantitative study in 1900. The bracts, 
problems e.. 
