60 



The former method may be called self- 

 pollination, the latter cross-pollination. 

 It seems evident that flowers in general 

 have made every effort to secure cross- 

 pollination. This would seem to imply 

 that it is a better method for some reason, 

 although we may not be able to explain 

 why. Apparently, however, while flow- 

 ers in general have tried to secure cross- 

 pollination, they have not entirely aban- 

 doned the chances of self-pollination, so 

 that if one should fail the other may be 

 used. In this way it will be found that a 

 great many plants have two kinds of flow- 

 ers, the ordinary showy kind, and in addi- 

 tion to them inconspicuous flowers which 

 are never seen except by those acquainted 

 with their presence. For example, in the 

 common violet, in addition to those flow- 

 ers with which everyone is familiar, oth- 

 ers are developed which are concealed by 

 the cluster of leaves, which never open, 

 but which are able to produce very well 

 developed seeds. 



With nectar and pollen provided as 

 food, and with odor and color notifying 

 the insects of their presence, it remains to 

 be noted that the suitable insects are those 

 which fly. A creeping insect is of no 

 avail in the work of pollination, since the 

 pollen will be rubbed from its body as it 

 crawls from one flower to the next. How 

 the flowers ward off the visits of creeping 

 insects, which are attracted as well as the 

 flying ones to the food provided, will be 

 described in a subsequent paper. 



A good illustration of the workings of 

 insect pollination may be found in the 

 sweet pea, or in any member of the pea 

 family. The flower has a rough resem- 

 blance to a butterfly, whose projecting 

 body is represented by a structure like 

 the keel of a boat. In this keel is a clus- 

 ter of stamens, and also the pistil with its 

 stigma at the top. While lying in this 

 keel the stamens shed their pollen upon 

 the style, which usually has hairs or some 

 sticky surface to receive it. Accordingly 

 the style bears the stigma on top and 

 masses of pollen stuck to its sides below. 

 An insect being attracted to such a flower 

 naturally lands upon the keel as upon a 

 shelf, with its head toward the center of 

 the flower, where the nectar is deposited. 

 If the insect is heavy enough the weight 



of its body pushes down the keel, but the 

 contained style is anchored, so that it 

 seems to dart out, and strikes the insect's 

 body, first with the stigma at the tip, and 

 then glancing along rubs its side against 

 the body of the insect. The insect flies 

 away with pollen rubbed upon its body, 

 and when it goes through the same per- 

 formance at another flower, the new stig- 

 ma strikes it first and gets some of the 

 pollen, and then some more pollen is 

 smeared on, and so the pollen is carried 

 from one flower to the stigma of another 

 flower. It is easy to see the effect of the 

 weight of a heavy insect by pressing down 

 the keel with a pencil, when the style will 

 be seen to dart forth at the tip. 



Perhaps-one of the most common ways 

 of securing pollination is that in which 

 the pollen and stigma are not ready at 

 the same time in the same flower. The 

 pollen may be ready to shed, but the 

 stisfma is not ready to receive, or the re- 

 verse may be true. This would seem 

 very effective in preventing self-pollina- 

 tion. Illustrations of this kind are ex- 

 ceedingly numerous, but perhaps as com- 

 mon a one as any is furnished by the 

 great fireweed, Epilobium. It has a con- 

 spicuous purple flower, and if a patch of 

 the plants be examined the flowers will 

 be found in two conditions. In one set 

 the cluster of stamens will be found pro- 

 jecting straight out from the flower, while 

 the style with its stigma is turned back 

 out of the way under the flower. In the 

 other set the stamens, having shed their 

 pollen, are turned back behind the flower, 

 while the style has straightened up, and 

 the mature stigma holds the same posi- 

 tion that the anthers did the day before. 

 An insect, in visiting such a group, there- 

 fore, may fly straight towards a flower 

 whose stamens are projecting and shed- 

 ding, and its body will be dusted with the 

 pollen. If it now flies to a flower which is 

 a little older, whose stamens are out of 

 the way, but whose style is projecting, its 

 body carrying the pollen will strike the 

 stigma. In this way the pollen is very 

 effectively transferred from one flower to 

 another. 



It would be impossible to give any ade- 

 quate account of the subject of insect- 

 pollination in general, as it is an immense 



