INSECTS AND FLOWERS 227 



forces its way into the passage formed by the outer perianth 

 petal and the over-arching style. In so doing its back 

 comes into contact first with the stigmatic lip, which 

 scrapes off any pollen that may have been carried from 

 another bloom ; then with the anther of the stamen by 

 which more pollen is deposited. As the bee comes out of 

 the flower its back touches only that part of the stigmatic 

 lip which is unreceptive, so that immediate pollination is 

 impossible. There is nothing to prevent the insect from 

 entering another section of the same flower, or another 

 flower of the same plant ; but observation has shown that 

 it more often flies to one at a distance, and thus effects 

 cross-pollination. 



In flowers of the sage tribe, the pollinating mechanism 

 has been brought to a marvellous state of perfection. It 

 may be studied most easily in the handsome blue salvia 

 (Salvia patens), which is often cultivated in gardens. 

 Like the white dead-nettle, the flower has a broad lip and 

 a hood, but its internal structure is different. Two of the 

 four stamens are abortive. The other two have short 

 filaments, but the connective between the anther lobes 

 is enormously elongated. The lower lobe of each func- 

 tional anther contains no pollen, but serves with its fellow 

 to block up the entrance to the corolla tube. Thus, when 

 a bee thrusts its head into the tube to search for nectar, 

 it pushes against these abortive anther lobes, causes the 

 long arms of the connectives to descend, and thus brings 

 the pollen-bearing anther lobes into contact with its back. 

 In older flowers that have shed their pollen, the style of 

 the pistil lengthens and bends down so that the receptive 

 stigma grazes the bee's back at the exact spot touched by 

 the anthers of a younger bloom. 



Flowers of the pea tribe secure cross-fertilisation by 

 means of a piston apparatus which pumps pollen on to 



