POLLINATION AND FERTILIZATION 



129 



FIG. 117. Head of Pronuba 

 moth. Magnified 



p, mass of pollen held in posi- 

 tion hy spinous appendages of 

 the moth's head 



the moth runs to the top of the pistil, as shown in Fig. 116, 

 uncoils the organs which hold the pollen mass, and with 



her tongue tlirusts the pollen vigor- 

 ously into the stigmatic opening for 

 several seconds. As the stigma is 

 usually pollinated after every depo- 

 sition of an egg, in cases where ten 

 or a dozen eggs are introduced into a 

 single pistil it is pollinated as many 

 times. After the hatching of the 

 eggs, each little grub that is pro- 

 duced from them eats up the ovule in 

 which 

 it was 

 depos- 

 ited, leaving, however, many 

 other ovules to mature into 

 seeds. It then bores its way out 

 through the capsule, drops to 

 the earth, and makes a cocoon of 

 silk a few inches underground. 

 It probably does not assume the 

 form of the adult (winged) in- 

 sect until near the next bloom- 

 ing time of the yuccas. 



The relations of the yucca 

 moth to the plant afford a most 

 remarkable example of cooper- 

 ation between a plant and one 

 of the lower animals. Without 

 pollination by the moth, yuccas 

 produce no seeds, while, on the other hand, without yucca 

 capsules and their contents the larvae hatched from the eggs 

 of the moth would starve. 1 



1 See Proceedings of the American Association for the Advancement oj 

 Science, 1880, Vol. XXIX, paper entitled " Further Notes on the Pollination 



FIG. 118. Pod of a tree yucca 



p, perforations caused by escape of 

 larva of yucca moth. Somewhat 

 reduced. After Thirteenth Annual 

 Report of Missouri Botanical Garden 



