i 6 Flowers and their Unbidden Guests. 



so many plants with bell-shaped or drooping flowers 

 are provided with certain defensive contrivances, is 

 that they jpay he able to keep off caterpillars from 

 seeking in them a snug corner for their webs and 

 transformations, and thus interfering with the func- 

 tions of the floral organs. 



Among the insects which have a soft outer skin, the 

 wingless aphides require special notice. We usually 

 find them in large numbers, and closely thronged, on 

 the under side of the leaves, and on the stalks of the 

 flowers and inflorescences. In flowers themselves they 

 are only rarely to be met with, because there are special 

 contrivances to prevent their access. If one transfers 

 them to the perianth, or to other parts of the flower, 

 they immediately thrust their rostrum into the juicy 

 tissue, which shows that the petals would be perfectly 

 acceptable to them. If placed on villous or tomentose, 

 or upon bristly and prickly, leaves, they behave most 

 awkwardly. They remain with their long legs hanging 

 between the hairs, or injure themselves by their help- 

 less movements on the sharp points of the trichomes 

 and teeth of the leaves. Leaves, and groups of leaves, 

 clothed with such defences, are therefore most carefully 

 avoided by them, and this explains why the colonies of 

 wingless aphides never advance farther up the stems 

 and flower-stalks than the involucres and calyces, ■ 

 when these are clothed with woolly or matted hairs, 

 or with bristles and prickles. 



