INTRODUCTION 25 
with the petals spread widely out. The next 
morning, however, the flowers appear to wilt; if 
the day is cool and cloudy they will only partially 
roll up, but if the day is cloudless and hot they 
seem completely to collapse. 
The odor of the Evening Primrose is given off 
to the greatest extent in the evening, when various 
long-tongued moths are abroad in search of the 
nectar which is secreted in the long calyx-tubes of 
the blossoms. Attracted by the odor the moths 
easily find the bright yellow flowers. They thrust 
their tongues behind the stamens and stigma to 
reach the nectar. Some of the stringy, adhesive 
pollen is thus dusted upon their mouth parts and 
carried from flower to flower; when it comes in 
contact with a viscid stigma it adheres to it. 
In this way the moths perform the useful office 
of cross-pollination, the carrying of pollen from 
the anthers of one blossom to the stigmas of 
another. 
Besides the moths which thus visit the blossoms 
in the evening there are a number of bees and 
flies that may be found upon the flowers in the 
daytime; some of these come for nectar and 
some for pollen. They probably assist in cross- 
pollination to a considerable extent. 
There are certain bumble-bees, however, which 
are not useful as visitors to the Evening Prim- 
rose, for, instead of entering at the mouth of the 
