362 FOUNDATIONS OF BOTANY 



sepals or petals prolonged into spurs, like the nasturtium 

 and the columbine, are inaccessible to most insects except 

 those which have a tongue or a sucking-tube long enough 

 to reach to the nectary at the bottom of the spur. The 

 large sphinx moth, shown in Fig. 254, which is a common 

 visitor to the flowers of the evening primrose, is an 

 example of an insect especially adapted to reach deep into 

 long tubular flowers. 



A little search among flowers, such as those of the 

 columbine or the foxglove, will usually disclose many 

 which have had the corolla bitten through by bees, which 

 are unable to get at the nectar by fair means or unwilling 

 to take the trouble to do so ; and they therefore steal it. 



433, Bird-Pollinated Flowers. Some flowers with very 

 long tubular corollas depend entirely upon birds to carry 

 their pollen for them. Among garden flowers the gladi- 

 olus, the scarlet salvia, and the trumpet honeysuckle are 

 largely dependent upon humming-birds for their pollination. 

 The wild balsam or jewel-weed and the trumpet-creeper 

 (Plate X) are also favorite flowers of the humming-bird. 



434, Prevention of Self -Fertilization. Dioecious flowers 

 are of course quite incapable of self-pollination. Pistillate 

 monoecious flowers may be pollinated by staminate ones 

 on the same plant, but this does not secure as good seed 

 as is secured by having pollen brought to the pistil from 

 a different plant of the same kind. 



In perfect flowers self-pollination would commonly occur 

 unless it were prevented by the action of the essential 

 organs or by something in the structure of the flower. In 

 reality many flowers which at first sight would appear to 

 be designed to secure self-pollination are almost or quite 



