MESSMATES, MUTUALISTS, AND PARASITES 89 



the slimy visitors crawl, transferring the pollen from one blossom 

 to another. 



The Humming- Birds of America, and the little Sun- Birds of 

 Africa, which resemble them in appearance, suck nectar while on 

 the wing from certain flowers. Regarding bird-pollinated forms, 

 Scott- Elliot, who made a special study of the subject in South 

 Africa, speaks as follows (in Nature Studies]: " Many tropical 

 flowers, such as the Banana, or the beautiful Lobelia cardinalis, 

 are visited by the Sun- Birds and Humming- Birds. A great 

 proportion of these flowers have a scarlet colour, and a curved 

 tube which exactly fits the head and beak of the bird. Others, 

 which are visited by these beautiful and lively creatures, have the 

 flowers massed together in large cup-shaped heads, such as the 

 Proteas, or Sugarbush of South Africa. The bird stands on 

 the edge of this cup and plunges its beak into the mass of honey 

 flowers which fills it. There are no bird flowers in the British 

 Flora, at least so far as the writer's knowledge goes ; but sparrows 

 can be seen to dip their beaks into the heads of the Ragwort, after 

 insects, and it is very likely that the flower-haunting habits of the 

 Sun- Birds began in this way." One of the bird-pollinated African 

 forms {Melianthus major] is represented in fig. 1080. 



Few observations have been made upon cross-pollination by 

 mammals, but some tropical Bats are supposed to further the 

 transference of pollen, and Kerner suggests that the same kind 

 office is discharged by Kangaroos for Dryandra bushes. The 

 flowers in the latter case are at a suitable height above the ground, 

 and are arranged round the edge of a sort of cup, into which a 

 fluid resembling sour milk trickles down from them. It is 

 not improbable that the little Long-Snouted Phalanger (Tarsipes 

 rostratus, see vol. ii, p. 181) transports the pollen of the flowers 

 which it constantly visits. 



Prevention of Self -Pollination. The various arrangements re- 

 lated to cross-pollination have been so evolved that they also, at 

 least for some time, prevent self-pollination. It may be that a 

 particular flower contains stamens only or a pistil only, and these 

 distinct staminate and pistillate flowers may either be on the same 

 plant (e.g. Spurges, Euphorbia) or on different plants (e.g. Wil- 

 lows, Salix). And even where stamens and pistil are present in 

 the same flower the pollen is commonly produced before the stigma 

 is mature, or, more rarely, the stigma is first ready. Of other 



