236 A BOOK OF INSECTS 



ferous hoods situated in front of each anther. As a leg is 

 drawn upward one of its claws, hairs, or spines frequently 

 catches in a V-shaped fissure and is guided along a slit to 

 a notched disc, or corpuscle. This disc clings to the leg 

 of the insect, which carries off by means of the disc a pair 

 of pollen-masses or pollinia. When first removed from 

 their enclosing pockets, or anthers, these thin spatulate 

 pollinia lie each pair in the same plane, but in a few 

 minutes the pollinia twist on their stalks and come face 

 to face in such a way that one of them can be easily 

 introduced into the stigmatic chamber of a new flower 

 visited by the insect. Then the struggles of the insect 

 ordinarily break the stem, or retinaculum, of the pollinium 

 and free the insect. Often, however, the insect loses a 

 leg or else is permanently entrapped, particularly in the 

 case of such large-flowered milkweeds as Asclepias cor- 

 nuti, which often captures bees, flies, and moths of con- 

 siderable size." In this way certain Asclepiads, especially 

 those which are cultivated in regions to which they are 

 not indigenous, have come to be called " cruel plants." 

 It has been truly said, however, that Nature's broad 

 methods are not exempt from occasional contretemps. 

 When these flowers are visited by powerful insects, 

 such as large humble-bees or wasps, the plan works to 

 perfection ; but when the mechanism is tampered with by 

 weaklings, they have to pay the penalty of their rashness. 

 There is one point connected with the pollination of 

 flowers that we must not overlook, namely, that certain 

 insects, attracted in the first instance by the promise of 

 nectar, remain to lay their eggs either upon or close to 

 the flower. This is the case, for example, with night- 

 flying moths of the genus Dianthoecia, the caterpillars of 

 which feed within the seed-capsules of the well-known 

 red and white campions — plants of the genus Silene and 



