THE WELCOME OF THE FLOWERS 



389 



between it and the sides of the tube. Insects are attracted from a distance 



by the crimson spikes of 



flowers, and are guided on 



their way to the honey by 



the dark red colour of the 



inner surface of the calyx 



and by the dark lines in the 



middle of each petal. These 



insects are caused to perform 



regular cross-pollination by 



the trimorphism of the 



flowers, which forms the 



most remarkable feature of 



the plant." 



The arrangements in 

 Nature for securing the 

 cross-fertilization of plants 

 are by no means exhausted 

 with the phenomena of di- 

 chogamy and heterostyly. 

 These provisions are doubt- 

 less the rule among insect- 

 pollinated flowers, but there 

 are innumerable exceptions 

 to the rule ; and, moreover, 

 all cross-fertilized plants do 

 not owe their pollination to 

 insect agency. Other ani- 

 mals, such as snails and 

 birds, sometimes perform 

 this office ; and in a large 

 number of cases wind and 

 water are the pollen-carriers. 

 For the present, however, 

 we may confine ourselves 

 to flowers that are pollinated 

 by insects. 



We have already shown 

 that many flowers are speci- 

 ally adapted, either by their 

 form or mechanism, for the 

 visit of certain insects ; and 

 further, that the colours, scents, and nectareous sweets of such flowers act 

 as lures to the guests that are wanted. The flower, indeed, as a talented 



Sle P- 



FIG. 478. BIRD'S-EYE PRIMROSE (Primula farinosa). 



A beautiful plant of northern moors and meadows with lilac-coloured 

 flowers. Dimorphic like the Common Primrose. 



