i 4 4 THE DARWINIAN THEORY 



pollen, not from the same flower, but from a 

 different flower or plant. This cross fertilisation is 

 always highly beneficial and often absolutely 

 essential. It is effected mainly by the agency of 

 insects, especially bees, flies, and butterflies. These 

 are induced to visit the flowers by bribes of honey 

 secreted by the flower in such a position that, in 

 order to reach it, the insect must brush against the 

 anthers and get dusted with the pollen, by which, 

 on visiting a second flower, fertilisation is effected. 



The purpose of the coloured part of the flower is 

 to form a conspicuous advertisement to insects of 

 places where honey is to be found ; and more 

 detailed markings in the flower direct the insect 

 towards the store of honey. Curiously ingenious 

 contrivances are found in order to prevent self- 

 fertilisation, and to ensure that the insect shall effect 

 its work properly^ 



A familiar instance is that of Orchis mascula, the 

 spotted orchid, which is abundant in meadows and 

 in damp places in open woods. This consists of a 

 spike of flowers, the calyx of which is formed by 

 three coloured sepals, and the corolla by three 

 petals. One of the petals, called the labellum, is 

 larger than the others, and forms a sort of landing- 

 stage. This is prolonged backwards into a spur-like 

 nectary with spongy walls. The male organs 

 consist of one anther with two cells, each of which 

 contains a pollen mass. The ovary has three pistils, 

 united together and twisted,, ending above in two 

 almost confluent stigmas. The third stigma forms 

 the rostellum, a rounded projection overhanging the 



