RELATION TO ENVIRONMENT 



517 



That the development of the showy parts of the flower is cor- 

 related with the visits of insects is readily seen by comparing 



A 



B 



FIG. 484. A, B, Erodium cicutarium, self-pollinated stamens and pistil maturing 

 at the same time (enlarged). C, D, Pelargonium sp., cross-pollinated. In Pelar- 

 gonium, the stigma, st, is immature when the stamens shed their pollen. D, sta- 

 mens and pistil from an older flower, the stigma, st, receptive. 



closely related species of plants which differ in this respect. Some 

 species of Ranunculus, for example, like R. sceleratus, have insignifi- 

 cant flowers which are not visited by insects, while the showy species, 

 like R. acris or R. Californicus, 

 are freely visited by insects. 

 So, in the genus Geranium, the 

 inconspicuous flowers of G. molle 

 are self-fertilized, while the 

 showy flowers of the Crane's-bill 

 (G. maculatum) are adapted to 

 insect pollination. 



In the simpler entomophilous 

 flowers, like Ranunculus or Por- 

 tulaca, the petals are nearly 

 uniformly colored, but in more 

 specialized forms there may be 

 definite spots or streaks of 

 sharply contrasting colors, such 

 as the black markings in a Pansy, 

 or the spots in a Foxglove. 

 While the significance of these 

 markings is not in all cases clear, 

 it is pretty certain that they are 



st- 



FIG. 485. TropSBolum mujus. A, young 

 flower cut lengthwise to show the im- 

 mature pistil, st, and the position as- 

 sumed by the stamens as they discharge 

 the pollen. B, pistil, st, and stamens 

 from an older flower; the stigma is 

 open, but the stamens have discharged 

 their pollen. 



in some cases guides to the nec- 

 taries, or honey-secreting organs 

 of the flower. 



The color of the flower is often associated with its attractiveness 

 to special insects or birds. Yellow is probably the commonest, and 

 perhaps the most primitive color, and next to this, white; blue, 



