128 THE FACTORS [Part I 



in allogamous flower-mechanisms (about 10 %), as well as a much more consider- 

 able increase in autogamy (about 15 %). 



The conditions of pollination in extreme arctic countries have been 

 investigated in Greenland by Warming. Insect-visits appeared to be 

 very rare. Anemophily and autogamy are correspondingly strongly, 

 and entomophily is weakly developed. Many flowers that are markedly 

 entomophilous elsewhere show a strong tendency to self-pollination ; for 

 example, those of Mertensia maritima, the flowers of which are smaller 

 in Greenland than in Scandinavia, of Azalea procumbens, Vaccinium 

 Vitis-Idaea var. pumila, Bartsia alpina, Thymus Serpyllum, Menyanthes 

 trifoliata, Pyrola grandiflora. In spite of the scarcity of insects, the 

 allurements are not more strongly marked than when a rich insect 

 fauna exists, although this is contrary to an opinion that has been 

 repeatedly expressed. 



Vegetative multiplication is strongly developed in Greenland, especially in 

 plants in which self-pollination takes place with difficulty or to a slight extent : 

 ' In Greenland, which is poor in insects, the more entomophilous a species may 

 be, the more it adapts itself to multiplication by vegetative means, whereas 

 autogamous plants can dispense with this kind of propagation, and actually do 

 dispense with it ' (Warming). 



The conditions of pollination have often been cited in explanation of 

 the peculiarities of insular floras. Wallace, especially, has tried to connect 

 the presence, absence, or rarity of brightly coloured flowers on islands 

 with the fauna. Thus on the islands of the eastern part of the South 

 Pacific Ocean, for example in Tahiti, insects, especially Lepidoptera and 

 bees, are rare : to this circumstance the poverty of the local flora in 

 entomophilous flowers, especially in brightly coloured ones, and the 

 prevalence of ferns have been ascribed. On the western islands, for 

 example in Fiji, butterflies are more numerous and have produced 

 through selection a greater number of brightly coloured flowers. The 

 flowers of the Galapagos have such inconspicuous flowers, that Darwin 

 could only after a long time convince himself that they nearly all 

 blossomed during his visit. As a matter of fact small Diptera and 

 Hymenoptera are the only representatives of the insect-world on these 

 islands. 



Such tentative explanations are certainly interesting and suggestive ; but 

 yet it need hardly be stated, that the above peculiarities are explicable, not 

 merely by the conditions of pollination, but by taking into consideration 

 also historical and climatic factors. Moreover, Wallace's views chiefly 

 rest on the incomplete information and collections of other biologists 

 whose investigations scarcely lay in this direction, and they have already 

 been refuted in many very important cases. Thus Wallace has described 



