RELATION TO ENVIRONMENT 525 



the sunbirds and honeysuckers are also agents in pollination. Most 

 humming-bird flowers are tubular in form and vivid red in color, the 

 flowers drooping or resting horizontally, so that they can be reached 

 by the slender tongue of the bird as it hovers before the flower. 

 Although but a single species of humming-bird occurs in the North- 

 eastern states, a number of flowers are especially adapted to its 

 visits. Of these the Coral-honeysuckle (Lonicera sempervirens), Col- 

 umbine (Aquilegia Canadensis), Cardinal-flower (Lobelia cardinalis), 

 Monarda didyma, Trumpet-creeper (Tecoma radicans), may be men- 

 tioned. In California the number of humming-birds is much greater, 

 and there is a corresponding increase in the number of flowers 

 adapted to their visits. Among the characteristic forms are the Scar- 

 let-currant (JRibes speciosum, Fig. 492), various species of Castilleia, 

 Zauscl^neria Calif oi-nica, Mimulus cardinalis, probably also the scarlet 

 species of Pentstemon, Gilia, Silene, etc. 



Of garden flowers, the Cannas, Scarlet-sage (Salvia splendens), and 

 Fuchsias are all humming-bird flowers. 



Heterostylism 



A peculiar arrangement for insuring cross-pollination occurs in 

 the so-called heterostyled flowers. In these there are two, and 

 sometimes three, types of flowers, differing in the relative length 

 of the pistil and stamens. The long-styled flowers have short sta- 

 mens, and vice versa. Where three lengths of the pistil occur, as 

 in Lythrum salicaria and Pontederia cordata, there are two sets of 

 stamens in each flower, corresponding in length to the other pistils, 

 so that the part of the body of the insect which comes in con- 

 tact with the stamens of a certain length will deposit it upon the 

 pistil of corresponding length in another flower. In these trimor- 

 phous flowers it has been found that the size of the pollen-grains 

 differs greatly in the long and short stamens, and the long-styled 

 flowers are only imperfectly fertilized by the pollen from the shorter 

 stamens. Of dimorphous flowers, or those with two lengths of 

 pistil, may be mentioned various species of Primula (Fig. 488), many 

 Borraginacese, like Myosotis and Mertensia; Epigcea repens, and 

 others. In the California Poppy, Eschscholtzia Californica, the flow- 

 ers are imperfectly heterostyled, longer styles being present in 

 some flowers, and adapted to cross-pollination, while the short ones 

 may be self-pollinated. 



Autogamy 



While most showy flowers are adapted to cross-pollination, it not 

 infrequently happens that they are capable of self-pollination in 



