120 BOTANY 



bodies, slippers, or spurs, either on the receptacle or the 

 perianth leaves. Irregularity of form of the calyx or 

 corolla was thus caused. Markings on the individual 

 sepals or petals followed, which directed the attention of 

 the insect, usually a wasp or bee, to the hidden store. 

 The honey became hidden in such a way that to reach it 

 the visitor brought some definite part of its person into 

 contact with the stamens, and on visiting another 

 flower touched the stigma with the same region. The 

 influence of colour and of fragrance were brought to bear 

 upon the insect visitors with similar results, the whole 

 mechanism of any particular flower being correlated 

 with the habit of some appropriate insect. 



The mechanisms of some flowers at the present time 

 are even more complete than this. As cross-pollination 

 is preferable to self-pollination, the flower is adapted 

 to some visitor to secure it; but as self-pollination is 

 better than none at all, if the insect mechanism should 

 fail to act, the stigma is in some way brought into 

 contact with the stamens of the same flower. 



The apparent ease with which self-pollination of 

 almost every flower can be brought about has led in 

 many cases to a peculiar modification to secure the 

 advantages of crossing. This consists in the maturing 

 of the stamens and the stigmas of a flower at different 

 times, so that if self-pollination should take place there 

 would be no result therefrom. This condition is known 

 as dichogamy ; flowers whose stamens mature before 

 their carpels are said to be protandrous ; those in 

 which the condition is reversed are proterogynous. 



It is of course obvious that cross-pollination is the 

 only possible method in the cases of those plants which 

 bear pistillate and staminate flowers. 



The cones of the fir trees are pollinated by wind. 

 When the cone is ripe its leaves separate a little from 

 each other so that the pollen grains, blown in large 



