200 



Introduction to Botany. 



tions will not be understood until subsequent developments 

 have been followed. Since the process of pollination has 

 been so thoroughly done, most of the numerous ovules 

 become fertilized and the seeds begin their development. 



In the meantime the moth 

 eggs hatch into larvae, 

 which find their food in 

 the developing seeds. But 

 the seeds are so numerous 

 that the larvae reach their 

 growth, gnaw a hole in 

 the seed-pod and escape, 

 while many uninjured 

 seeds still remain in the 

 pod. The larva spins a 

 thread by which it de- 

 scends to the ground, and, 

 burrowing beneath the sur- 

 face, it passes the winter in 

 its pupal state, emerging as 

 a. fully developed moth at the time of the flowering of the 

 Yucca the following summer. 



It appears that the mature moth takes no food, unless 

 it secures some of the nectar of the Yucca blossoms in 

 which it is wont to pass the day, with its head close to 

 the bottom of the flower where the nectar is excreted. It 

 does not eat the pollen which it gathers, and it seems cer- 

 tain that it is prompted to place the pollen in the stigmatic 

 tube after each act of oviposition solely by the instinct to 

 provide for its young ; for it is readily understood that if 

 the ovules are not fertilized the seeds would not develop 

 and the larvse would be without food. 



The Yucca flower, instead of having elaborate devices 



Fig. 119. 



Pronuba moth rubbing pollen down the 

 stigmatic tube of a yucca flower. Flash- 

 light photograph taken about 8.30 P.M. 



