i86 



GROWTH AND WORK OF PLANTS 



insect. The pollen is somewhat sticky and without some aid 

 could not be deposited in the funnel-shaped stigma. The 

 moth resting quietly in the flower during the day, at dusk 

 crowds down over the stamens, digs out some of the pollen mass 

 with her foot, passes down on the ovary over one of the furrows 

 directly over where the ovules are located, pierces the ovary with 

 her ovipositor and plants an egg in an ovule. Then she passes 



Fig. 138. 



Longitudinal section of an 

 ovary of Yucca, showing the 

 funnel-shaped stigmatic opening 

 (s) , and the rows of ovules attached 

 to the wall (o). After Riley and 

 Trelease. 



A*. 



Fig- 139- 



The position of Pronuba on the 

 stamen of Yucca when collecting 

 pollen and when thrusting it into 

 the stigmatic funnel. After Riley 

 and Trelease. 



on to the end of the pistil and crowds the pollen into the funnel- 

 shaped opening of the stigma. She repeats this process several 

 times, depositing several eggs and placing an abundance of 

 pollen in the stigma, which insures the development of a large 

 number of seeds, some of which can be used for food by the 

 young larvae. 



CROSS-POLLINATION BY THE WIND. 

 300. Wind pollination. This takes place in quite a variety 

 of plants, it is the chief method among the grasses, cereals, Indian 



