THE YUCCA MOTH AND YUCCA POLLINATION. 177 



the tongue are so often separated at tip, and so weakly joined 

 throughout, as to raise the question, in connection with a some- 

 what imperfect alimentary canal, as to whether the moth feeds at 

 all, and to suggest that the rather strong tongue, otherwise, as- 

 sists pollination. 



No sooner is the ovipositor withdrawn into the abdomen than 

 the moth runs up to the top of the pistil, thrusts the pollen into 

 the stigmatic opening, and works her head rapidly the motion 



Y\a. 7. Flowek of Yucca, with near petals removed to show normal position of Pronuba in 



ovipositing. 



being mostly up and down and lasting several seconds. She 

 works with a vigor that would indicate combined pleasure and 

 purpose, and makes every effort to force the pollen into the tube, 

 thrusting it ordinarily from the base of one of the three primary 

 clefts of the style. After the more vigorous motions of thrusting 

 the pollen into the tube, she frequently rests in comparative 

 quiet, working her tongue in the tube sometimes for four or five 

 minutes together, but ordinarily the act of pollination ceases with 

 the few vigorous thrusts already described. The importance of 

 this act will be better appreciated when I state that numerous ex- 

 periments in artificial or brush pollination have shown that effect- 

 ive fertilization in Yucca filamentosa is by no means an easy 

 matter, and that it rarely takes place as effectively as through 

 the actions of Pronuba. 



This carrying of the pollen to the stigma generally follows 

 every act of oviposition, so that where ten or a dozen eggs are 

 consigned to a single pistil, the stigma will be so many times be- 

 pollened. 



The egg of Pronuba is an extremely delicate, thread-like 

 structure, averaging 1*5 millimetre in length and less than O'l 

 millimetre (Fig. 9, c) in diameter, tapering at the base and en- 

 voi-. XLI. 15 



