RELATIVES OF THE HERB ROBERT 149 
All these differences in the petals, including their 
longer or shorter duration, seem to depend to some 
extent upon whether the plants grow in the sun or 
the shade. 
The flowers with the three long petals are, I think, 
to be found as a rule in the more sunny and open 
‘places, and those in which they are all of the same size 
in the shadier ; and I will therefore use the word sun 
or shade, as the case may be, to distinguish the two 
forms, but without implying exclusive restriction 
to either kind of place. 
It is the former that are capable of retaining their 
petals through the night and into the next day: the 
shade flowers, on the other hand, seem always to lose 
them before or during the afternoon, agrecing in this 
respect with those of the Shining Cranesbill, although 
the habit is not so strikingly noticeable in that species. 
The probable explanation is that the shade flowers 
are considerably less adapted to a cross, and resort 
more quickly than the others to self-pollination. 
This suggestion is supported by the relative 
maturity of the sexual organs in each form of flower. 
Generally I could detect no separation in time in 
the blossoms of the shade plants, but whenever it was 
possible to make sure of any difference in such a short- 
lived flower it was the stigmas that matured first, 
whereas in the sun blossoms separation is the rule, but 
it is then the anthers that shed their grains before 
the stigmas become receptive. 
Thus the plants in the sun make the higher bid 
for cross-pollination both in the marked separation 
of the sexes and the longer life of the petals. 
I do not know whether the earlier maturity of 
the anthers gives them any additional advantage in 
