METHODS OF POLLINA TION 



187 



corn, the amentiferous trees and shrubs (those bearing catkins), 

 and among the conifers. The pollen is very abundant, dry and 

 "dusty," and is easily scattered by the wind. Whoever has 

 been in a cornfield at the time of pollination will realize this. 

 In the pines among the conifers, the pistillate cone stands erect 

 and the scales flare outward during 

 pollination. The pollen is caught 

 on these scales and rolls down to 

 the lower end, where it is caught 

 in a viscid substance in the micro- 

 pyle of the ovule. 



CROSS-POLLINATION BY 

 INSECTS. 



301. How insects are attracted 

 to flowers. In order to secure 

 cross-pollination through the aid of 

 insects, the insects must be lured 

 or attracted to the flowers for some 

 highly prized food. Provision of 

 food is made in the nectar which is 

 developed in special nectar glands, 

 or nectaries, in these flowers. The 

 odor from flowers probably has more 

 influence in attracting insects to 

 them than anything else. This is very striking in the case of 

 night-blooming flowers, which usually have strong fragant odors 

 and attract the moths which fly at night. In addition most 

 flowers adapted for cross-pollination by insects have showy parts, 

 which by their size and color attract the insects, and stand for 

 them as a sign of those flowers which produce nectar. In the 

 larger number of cases the petals are the showy parts of the flower. 

 Sometimes it is the sepals, especially in the apetalous flowers, 

 as in the marsh marigold, etc. In other cases the bracts of the 

 flowers are colored and showy, as in the flowering dogwood. In 

 many composite flowers it is the ray flowers which are showy 



Fig. 140. 



A mature capsule of Yucca, showing 

 perforations made by larvae of Pronuba 

 in escaping. After Riley and Trelease. 



