336 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
It will also readily be recognized that partial variability may 
be complicated further by the development of homologous organs 
or parts of the organs at different times: the variations may involve 
organs which mature over a somewhat extended period either in 
different years or in a single season. A marked example of the 
latter is to be seen in perennials which produce a new crop of 
leaves, flowers, and fruit in consecutive years, giving inter-year . 
variations which may involve the age of the individual. Further- 
more, annuals, biennials, and perennials most frequently show a 
more or less extended period of development in a single season, 
during which homologous organs come into maturity with quite 
different positions on a plant and at quite different times. 
АП these aspects or factors of partial variability complicate 
the adequate determination of the expression of the capacities of 
an organism, and, it would seem, are factors that must be consid- 
ered in an analysis of individual variability upon which any dis- 
cussion of variation, heredity, or selection is based. 
Furthermore, partial variability (as well as individual vari- 
ability) may involve different kinds or grades of characters such 
as: (т) size, as of seeds, fruit, etc.; (2) chemical properties, as 
color, sugar-content, etc.; (3) number of homologous organs 
grouped together in a specialized structure such as the number of 
flowers in an inflorescence or the number of petals or sepals in a 
flower. Bateson has used the term ''meristic" to apply to varia- 
tion in number, as distinguished from substantive (such as color) 
variations which are more qualitative. The term ''meristic" is, 
however, not applied solely to partial variability. 
Further, partial variability may involve elements of differen- 
tiation which may not be suspected from random observations 
and collections of data, but which may constitute a source of 
error. The relation of fluctuating variability to differentiation 
is by no means clear, as the discussions of Pearson (от and 'o2a) 
and Bateson ('o3) indicate. Very generally, however, the element 
of differentiation has been entirely disregarded in statistical 
studies of characters exhibiting wide partial variability. 
The development of varying numbers of flowers in the different 
heads produced on a plant of a species of Compositae illustrates a 
type of partial meristic variation in the total number of flowers 
