RECIPROCAL RELATIONS 83 



nity which did not naturally occur before the soil had been drawn into 

 the service of man ; and the species which now occur in vast numbers, 

 and form a community with its own special stamp and economy, must 

 previously have been scattered singly at the edge of the forest or in other 

 open places. 1 



Further information concerning interference by man will be given in 

 Section XVII. 



CHAPTER XXIV. SYMBIOSIS 2 OF PLANTS WITH ANIMALS 



MODERN biological investigations, 3 to which Darwin's works gave 

 the impulse, have elucidated the manifold and complex relations sub- 

 sisting between the plants and animals that form one community, and 

 have demonstrated the adaptations of plants to animals and the converse. 



From a floristic standpoint we may note between the distributional 

 area of certain plants and animals a connexion which is due to 

 exact reciprocal adaptation : as examples may be cited : Aconitum and 

 Bombus 4 ; Vanilla, which was introduced into Mauritius at the com- 

 mencement of the eighteenth century, but could be made to bear fruit 

 only by artificial pollination, because the proper pollinating insects were 

 lacking ; Angraecum sesquipedale, which is undoubtedly adapted to a 

 moth with an immensely long proboscis ; Yucca filamentosa, dependent 

 for pollination upon Pronuba yuccasella. 5 



Attention may also be drawn to the utterly different parts played 

 by entomophilous and anemophilous flowers in the physiognomy of the 

 whole plant-community and the landscape. Trees of the northern 

 forests are anemophilous, those of the tropical ones are mainly entomo- 

 philous, and there thus arise those differences in floral beauty that give 

 to the forest an entirely distinct appearance. 



Many oceanic isles, the Galapagos Isles for instance, are poor in 

 spermophytes with highly coloured blossoms, but abound in ferns and 

 plants with small or inconspicuous flowers : apparently this is to be 

 correlated with the scantiness of the insect fauna. 6 



But other matters have also to be taken into consideration. All 

 structural features serving to protect plants against animals : poisons, 

 bitter bodies, raphides, stinging hairs, sharp bristles, and so on ; 7 the 

 reciprocal adaptations between insects and flowers ; structural features 

 enabling plants to utilize animals as agents dispersing their fruits (endozoic 

 dispersal of seeds in juicy and coloured fruits, epizoic dispersal of fruits 

 and seeds provided with hooks and glandular hairs, myrmecochorous 

 plants) 8 or even buds and parts of shoots ; symbiosis of ants and plants 



1 Warming, 1892. 



2 [A somewhat extended significance is here given to the term Symbiosis.] 



3 In this connexion may be mentioned the names of Axell, Beccari, Briquet, 

 Burkill, Delpino, Scott-Elliot, Hildebrand, Keller, Knuth, Lindman, Low, Ludwig, 

 MacLeod, H. Muller, A. F. W. Schimper, Schumann, Warming, Willis, and many 

 others. 



4 Kronfeld, 1890. 6 Riley, 1873, 1891 ; see also Knuth, 1904, iii, p. 130. 

 8 Wallace, 1880 ; but see M. G. Thomson, 1880. 



7 Stahl, 1904. 8 Sernander, 1901, 1906. 



G 2 



