44 THE FERTILISATION OF FLOWERS. [CHAP. 



spur. The bee on visiting the flower, alights on the 

 median petal (MP), and its weight, by depressing 

 the petals, probably forces the side of the spur (Sp) 

 against the anther processes (Ap), the effect of which 

 is to unlock the ring of anthers (A). The bee's head 

 also strikes against the stigma, which causes the loose 

 dry pollen to fall on the bee's face. On visiting 

 another flower this pollen will be deposited on the 

 under-surface of the stigma. It is remarkable that 

 in this species the pollen is dry and loose, whilst in 

 most entomophilous flowers it is sufficiently sticky to 

 adhere to the anthers, but in this case the bee does 

 not rub against the anther, therefore if the pollen 

 were not loose and dry, fertilisation could not take 

 place. 



In the pretty little Milkwort (Polygala vulgaris) 

 again, we have a different arrangement. The petals 

 form a tube to which the stamens are attached in tv/o 

 bundles near the top. Below these is the stigma, and 

 behind it a viscid disc. The proboscis of an insect 

 pushed down this tube in search of honey comes in 

 contact with the viscid disc, and is thus rendered 

 adhesive. When it is withdrawn it touches against 

 the anthers and carries off some of the pollen to be 

 deposited on another flower. 



In the Mallows (Malvd) we have good evidence 

 of the truth of the theory that the object of colour 

 in flowers is to attract insects. We have two species 

 of Mallows growing in the same locality, Malva 

 sylvestris and M. rotundifolia. Sylvestris is fertilised 

 by insects, rotundifolia fertilises itself, and is seldom 

 visited by insects. Sylvestris has large conspicuous 



