520 



BOTANY 



especially fitted to the long tongues of these insects, which are 

 frequently met with about these flowers, especially at dusk. Other 

 moths are also agents in pollinating nocturnal flowers. 



Preventions against Self-pollination. In the most specialized 

 entomophilous flowers self-pollination is often impossible, owing 

 either to the relative position of the stamens and pistil, or to 

 their maturing at different times. In the less specialized forms, 

 such as many species of Ranunculus, while the flowers are visited 

 by many insects which 

 usually effect cross- 

 fertilization, still, where 



B 



FIG. 489. Cytisus sp. A, 

 young flower. J5, flower 

 which has been visited by 

 a bee ; the keel, k, is pushed 

 down, exposing the sta- 

 mens and pistil, st. 



FIG. 490. 7m versicolor. A, flower showing the 

 position of the stamens, an, under the overarching 

 petaloid styles. B, under surface of the style, 

 showing position of stamen, an, and stigma, st. 



insect visits are pre- 

 vented, the flowers can 

 pollinate themselves. 

 It is otherwise with the more specialized flowers, especially with 

 most zygomorphic ones. In the showy species of Pelargonium 

 (Fig. 484), when the flower first opens, the five stigmatic lobes are 

 closed, and do not open until after the pollen has all been shed, so 

 that they must receive pollen from a younger flower, which can only 

 be done through the visits of insects. In Tropseolum (Fig. 485) the 

 same thing is true, and here the flower is more modified, the two 

 upper sepals being prolonged backward into a spur-shaped nectary, 

 which is accessible only to insects with long tongues, especially 

 bumblebees. Humming-birds are also frequent visitors of these 



