120 THE FACTORS [Part I 



i. GEOGRAPHICAL DISTRIBUTION OF THE ARRANGE- 

 MENTS FOR POLLINATION. 



By the investigations of K. Sprengel and Darwin, which have been so 

 wel] supplemented by those of Fritz and Hermann Miiller, Delpino, 

 Hildebrand, and many others, it has been definitely proved that many 

 flowers require for their pollination the assistance of certain animals, 

 sometimes insects, more rarely birds, and that they owe many of their 

 peculiarities to this circumstance. 



Numerous flowers are robbed and pollinated by the most varied visitors, 

 as their pollen and nectar are offered freely to all, or are easily accessible. 

 Other flowers are, in a greater or less degree, adapted to certain definite 

 visitors, either because their allurements presuppose characteristic tastes, 

 or the access to their nectar is only possible to visitors possessed of a 

 certain bodily shape or of certain faculties. When adaptations of the latter 

 kind are connected with animal forms of restricted distribution, the 

 presence or absence of such adaptations is characteristic of the vegetation 

 of definite districts. 



i. ORNITHOPHILOUS FLOWERS. 



The greatest phytogeographical interest, at least from the present point 

 of view of our knowledge, is attached to the adaptations of flowers to 

 pollination by birds, because birds that visit flowers are restricted to 

 certain definite districts. Chiefly three classes of birds come thus under 

 consideration — humming-birds (Trochilidae), sun-birds (Nectariniidae), and 

 honey-suckers (Meliphagidae), although individual birds of other families 

 also play the part of pollinators. 



Humming-birds are restricted to America. Only in the fantasy of 

 certain flower-biologists are they ever seen swarming round flowers in 

 Africa and Asia. Their importance as pollinators was first hypothetically 

 mentioned by Delpino, but first proved in 1870 by Fritz Miiller, who 

 observed humming-birds as pollinators on species of Combretum, Manettia, 

 and Passiflora, in Santa Catharina. Belt then wrote \ as a result of careful 

 observations in Nicaragua, the first complete descriptions of humming- 

 bird flowers. 



' Higher up the valley more trees were left standing, and amongst these small 

 flocks of other birds might often be found, one green with red head (Calliste 

 laviniae, Cass.) ; another shining green, with black head (Chlorophanes guatema- 

 lensis) ; and a third, beautiful black, blue and yellow, with a yellow head 



1 Belt, I, p. 128. 



