258 Non-Isolable Races. 
Here again there is no discernible correlation. I have 
obtained the same result in other years. From this we 
see that in this case at least selection must not be founded 
on the different flowers of a plant but on the individual 
plants. However, the possible influence of the various 
grades of branching independently of the number of 
petals remains to be investigated. 
But whereas no internal causes were found which 
determined the pleiopetaly in the individual flowers, the 
external causes could be discovered the more readily. 
This character follows the general rule ; for the higher 
the nutrition and the more favorable the environment 
the more petals are produced per flower. The following 
experiments and observations will prove this. 
I shall first refer to an observation for which un- 
fortunately I can give no numerical corroboration, but 
which may throw some light on the independence of the 
character of the flowers, of the order of branching. In 
the summer of 1892 when I examined all the flowers of 
my culture, and recorded the number of their petals twice 
a week, I was struck by the fact that the high numbers 
fell on particular days whilst on other days only low or 
intermediate numbers were observed. This would seem 
to indicate that during the development of the flowers 
in May and June pleiopetaly is influenced by weather 
conditions, in such a way that flowers which are in the 
susceptible period of their development during fine 
weather will produce more petals, quite independently 
of the order of the branch which bears them. 
This conclusion is supported by another set of obser- 
vations. In September 1892 the flowers, on the whole, 
produced more petals than they did in August of the 
same year. Or, to be more accurate, the number was greater 
