362 FOUNDATIONS OF BOTANY 
: sepals or petals prolonged into spurs, like the nasturtium 
and the columbine, are inaccessible to most insects except 
those which have a tongue or a sucking-tube long enough 
to reach to the nectary at the bottom of the spur. The 
large sphinx moth, shown in Fig. 254, which is a common 
visitor to the flowers of the evening primrose, is an 
example of an insect especially adapted to reach deep into 
long tubular flowers. 
A little search among flowers, such as those of the 
columbine or the foxglove, will usually disclose many 
which have had the corolla bitten through by bees, which 
are unable to get at the nectar by fair means or unwilling 
to take the trouble to do so; and they therefore steal it. 
433. Bird-Pollinated Flowers. — Some flowers with very 
long tubular corollas depend entirely upon birds to carry 
their pollen for them. Among garden flowers the gladi- 
olus, the scarlet salvia, and the trumpet honeysuckle are 
largely dependent upon humming-birds for their pollination. 
The wild balsam or jewel-weed and the trumpet-creeper 
(Plate X) are also favorite flowers of the humming-bird. 
434, Prevention of Self-Fertilization. — Dicecious flowers 
are of course quite incapable of self-pollination. Pistillate 
moncecious flowers may be pollinated by staminate ones 
on the same plant, but this does not secure as good seed 
as is secured by having pollen brought to the pistil from 
a different plant of the same kind. 
In perfect flowers self-pollination would commonly occur 
unless it were prevented by the action of the essential 
organs or by something in the structure of the flower. In 
reality many flowers which at first sight would appear to 
be designed to secure self-pollination are almost or quite 
