FERTILIZATION OF FLOWERS. 227 



and pea; in the two latter, the pollen is often shed before 

 the flower opens. Not so frequently the stigmas mature first, 

 as in the plantain (Fig. 121, G). 



In many flowers, the stamens, as they ripen, move so as to 

 place themselves directly before the entrance to the nectary, 

 where they are necessarily struck by any insect searching for 

 honey; after the pollen is shed, they move aside or bend 

 downward, and their place is taken by the pistil, so that an 

 insect which has come from a younger flower will strike the 

 part of the body previously dusted with pollen against the 

 stigma, and deposit the pollen upon it. This arrangement is 

 very beautifully seen in the nasturtium and larkspur (Fig. 

 99, J). 



The tubular flowers of the Sympetalce are especially adapted 

 for pollination by insects with long tongues, like the bees and 

 butterflies, and in most of these flowers the relative position 

 of the stamens and pistil is such as to ensure cross-fertiliza- 

 tion, which in the majority of them appears to be absolutely 

 dependent upon insect aid. 



The great orchid family is well known on account of the 

 singular form and brilliant colors of the flowers which have no 

 equals in these respects in the whole vegetable kingdom. As 

 might be expected, there are numerous contrivances for cross- 

 fertilization among them, some of which- are so extraordinary 

 as to be scarcely credible. With few exceptions the pollen is 

 so placed as to render its removal by insects necessary. One' 

 of the simpler contrivances is readily studied in the little' 

 spring-orchis (Fig. 89) or one of the Habenarias (Fig. 90, G). 

 In the first, the two pollen masses taper below where each is 

 attached to a viscid disc which is covered by a delicate mem- 

 brane. These discs are so placed that when an insect enters 

 the flower and thrusts its tongue into the spur of the flower, 

 its head is brought against the membrane covering the discs, 

 rupturing it so as to expose the disc which adheres firmly to 

 the head or tongue of the insect, the substance composing the 



