Insects and Flowers 567 



provided for it, as in the case of violets, where horn-like outgrowths from 

 the two lower stamens secrete the nectar and pour it into a cup formed by 

 the base of the lower petal. 



"The nectaries may occur on any part of the flower, but they are most 

 frequently found at the bases of the stamens, petals, and ovaries, and rarely 

 on the calyx. In the plum and peach they form a thick inner lining of 

 the cup-shaped receptacle. In nasturtiums the nectar is secreted in a long 

 spur from the calyx. 



"Some flowers of simple construction expose their nectar freely to all 

 sorts of insects, but others conceal it in various ways so that it is accessible 

 only to insects of certain kinds. A frequent device is to have some parts 

 of the corolla close over the way to the nectar so that small insects which 

 would not assist in cross-pollination are excluded, and only those which 

 are strong enough to push aside the barrier or have proboscides of proper 

 construction to thrust past it can obtain the nectar and accomplish the trans- 

 ference of the pollen." 



With nectar and pollen ready for the insect the plant has yet to advertise 

 its sweets, and for that brilliant colors and attractive odors are relied on. 

 An attractive odor for insects is not always pleasing to us: certain Araceae, 

 some Trilliums, and others have a carrion-like odor, combined with "dull 

 colors often marked with livid blotches or veins like dead animal bodies, and 

 these flowers attract flesh-flies and carrion-beetles which are the pollinating 

 agents." It appears from various experiments that odor is the chief factor 

 in attracting insects from a considerable distance, and that with the nearer 

 approach of the insect color becomes an important guide. Despite the 

 poor sight (formation of incomplete images, and this possible only within 

 certain limited focal distances) of insects they appear to distinguish colors 

 at distances where the forms of objects must be very indistinct to them. 

 Once attracted to the flower by odor or color, or by both, the pattern and 

 fine color streaks and spots play their part in guiding them to the nectaries. 

 (See discussion on p. 580 of the sight and color recognition of insects.) The 

 shape of the flower now has also its influence; this it is which compels the 

 visitor, in order to get at the nectar, to brush against the pollen, or the stigma, 

 or both as the case demands, and thus to render fairly its payment for the 

 special food provided. The particular shape and make-up, too, often have 

 reference to the necessity of keeping away illegitimate visitors, who would 

 drain the secreted stores without recompense. Small creeping insects, as 

 ants (very fond of nectar), thrips, and others may be shut out of the nectaries 

 by fine, stiff little hairs densely set in the throat of the flower-cup, like those 

 on the stamens of spiderwort or at the bases of the stamens of Cobcea scan- 

 dens, or may be denied access even to the flower itself by sticky glandular 

 hairs on the stem and leaves. I once counted nearly a hundred dead or 



