Insects and Flowers 
577 
municates with the cavity of a carpel. Accordingly, when pollen is once 
deposited on the inner surface of the main stigmatic tube, the pollen-tubes 
find easy access to the ovules in each of the three carpels. The pollen is 
sticky and hangs together in masses, so that it is not adapted to being carried 
by the wind, and it is apparently impossible for it to get to the stigmatic 
tube without some outside agent. 
“A small amount of nectar is secreted, but it is excreted at the very base 
of the pistil, so that insects seeking it would be far removed from the stigmas. 
Indeed, the low position of the nectar would seem rather to lead insects away 
from the stigmas. The flowers are borne in compound racemes high aloft 
on a strong woody shaft, and, because of their rather strong odor when new 
buds are opening in the evening and their white color, they are quite cer¬ 
tain to make their presence known to insects flying in the twilight. 
“If we take these facts as our clew and attentively watch these flowers 
about eight o’clock in the evening, the method of cross-pollination will be 
made clear. A white moth, known as the 
Pronuba-moth, is seen to mount a stamen, 
scrape together the sticky pollen, and 
pack it against the under side of its head 
by means of a spinous structure known 
as the maxillary tentacle, which seems 
to have been specially developed for this 
purpose, for in other moths it is a mere 
vestige. In gathering the pollen it hooks 
its tongue over the end of the stamen, 
evidently to secure a better hold. Having 
become well loaded with pollen, as shown 
in the photomicrograph of the moth’s 
head, it descends the stamen and flies 
to another flower. There it places itself 
on the pistil between two of the stamens 
(see Fig. 768) and thrusts a slender ovipositor through the wall of the ovary 
and into the cavity occupied by the ovules. 
“Having deposited an egg, it ascends the pistil, and by means of the 
maxillary tentacles and tongue, which at other times are coiled around the 
load of pollen, it rubs pollen down the inner surface of the stigmatic tube. 
Fig. 769 is a [drawing made from a] flashlight photograph of a moth performing 
this act. The moth then descends the pistil, and standing between another 
pair of stamens it deposits another egg within the ovary; then it ascends 
the pistil and rubs pollen on the stigmatic surface as before. This process is 
repeated until it may be that each of the six lines of ovules is provided with an 
egg, and the process of pollination has been as many times accomplished. 
Fig. 768.—Pronuba-moth depositing 
eggs in ovary of Yucca. (After 
Stevens; natural size.) 
