2o6 LIFE : OUTLINES OF GENERAL BIOLOGY 



being unable to make any new adjustment for securing adequate 

 fertilisation. 



But the question rises whether other visitors besides insects may 

 not effect pollination, and one's thoughts naturally travel to birds, 

 also creatures of the air. It has been known for many years that 

 certain birds acted as pollinators, but a recent investigation by 

 Dr. Otto Porsch has proved that the role of birds in this capacity 

 is much greater than has been hitherto realised. He finds tliat in 

 Java alone sixteen per cent, of the families of flowers have bird- 

 visited sjx'cies, and that these are pollinated by twentj'-two different 

 kinds of birtb^. 



Excluding all those birds that visit flowers in search of insects, 

 as their stomach contents prove, Porsch has evidence of i,6oo 

 different kinds of birds, in thirtj'-one families, that habitually act 

 as pollinators! They belong to such families as humming-birds, 

 honey-birds, and sun-birds; and what they are in search of is the 

 nectar. These flower-birds are usually small in size and strong on 

 the wing, so that they can land on the flower or poise before it like 

 humming-bird hawk-moths. They tend to have a longish pointed 

 bill and an elongated protrusible tongue, sometimes brushlike, 

 with which they can lick u^ the nectar. Birds usually require a 

 relatively large supply of water, and this is not always available in 

 the tropics. Hence the advantage of being able to tap the nectaries of 

 flowers. 



That the nectar is food as well as drink is obvious, and it often 

 has other valual)le components besides sugar. It has been proved 

 that some kinds of flower-birds keep to one particular type of 

 flower, and though they are not concerned with the pollen, they 

 carry it on their forehead from blossom to blossom. 



But just as there are special flower-birds, so there are special 

 bird-flowers, belonging to such types as honeysuckles, tropajolums, 

 fuchsias, gardenias, mallows, and irises. They tend to have con- 

 spicuous colours, including pure white, and long tubular corollas. 

 They are usually odourless, and will therefore make little appeal to 

 bees, which live very largely in a smell-world. They are particularly 

 characterised by the copiousness and liquidity of their nectar, and 

 some of them have very interesting adaptations that make it difficult 

 for the nectar-receptacles to overflow. There are no bird-flowers in 

 Kurc)|)e. and part of the explanation is that if a bird is a habitual 

 nectar-feeder it must be able to get supplies throughout the year. In 

 other words, bird- flowers and flower-birds are most likely to be found 

 in places with a perennial flowering season. This does not apply in 

 the same way to insects, which are mostly in an inactive state 

 throughout the winter. In any case, it has been proved, by Porsch 

 and others, that in warm countries an important r61e in pollination is 

 filled by nectar-sipping birds. 



