GENERAL CHARACTERS OF SUB-ORDER 411 



cium consists of ten slightly perigynous stamens, either all the 

 filaments are united (monadelphous), or nine are united and the 

 posterior or upper one free {diadelphous). The gynaecium is 

 superior, of one carpel, and contains one or many ovules. Fruit 

 generally a legume ; seeds with a firm leathery testa, exendo- 

 spermous ; the embryo possesses thick fleshy cotyledons. 



The cotyledons of the bean, vetch, and pea remain permanently 

 below ground, while others, such as the clover, sainfoin, and 

 lucerne, come above the ground soon after germination com- 

 mences. 



The flowers of the Papilionaceae are all specially adapted 

 for insect pollination. The 'standard' acts as a conspicuous 

 attractive banner. The ' wings ' and ' keel ' petals are often 

 interlocked near their bases in such a manner that when an 

 insect of sufficient weight alights on the ' wings ' the latter are 

 pressed downwards and these in turn depress the ' keel ' petals ; 

 the stamens, style, and stigma are by this movement forced out 

 at the apex of the ' keel,' and the pollen is brought into contact 

 with the underneath part of the insect's body. The insect 

 visiting another flower brings the pollen on its body into contact 

 with the stigma of the flower which, on account of its length and 

 position, is generally forced out first from the apex of the ' keel ' ; 

 cross-pollination is thus effected. 



Some plants, such as field and garden peas, sweet pea, common 

 and hairy vetch, dwarf kidney-bean, hop-clover, and hop-trefoil, 

 while undoubtedly possessing flowers specially adapted for insect- 

 pollination are capable of self-pollination, and are fertile and able 

 to produce seeds when insects are excluded. Others, such as 

 red, white and crimson clovers, scarlet-runner bean, and broad 

 bean are more or less sterile when insects are prevented from 

 visiting the flowers. 



All parts of the plants, and especially the seeds, contain 

 considerable quantities of nitrogenous substances, upon which 

 much of their feeding-value depends. 



