XI THE SPECIAL COLOURS OF PLANTS 321 



(Phorniium tenax), are cross-fertilised by birds ; while in Natal 

 the fine trumpet -creeper (Tecoma capensis) is fertilised by 

 Nectarineas. 



The great extent to which insect and bird agency is 

 necessary to flowers is well shown by the case of New 

 Zealand. The entire country is comparatively poor in species 

 of insects, especially in bees and butterflies which are the 

 chief flower fertilisers ; yet according to the researches of 

 local botanists no less than one -fourth of all the flowering 

 plants are incapable of self-fertilisation, and, therefore, wholly 

 dependent on insect or bird agency for the continuance of 

 the species. 



The facts as to the cross-fertilisation of flowers which have 

 now been very briefly summarised, taken in connection with 

 Darwin's experiments proving the increased vigour and fer- 

 tility given by cross -fertilisation, seem amply to justify his 

 aphorism that " Nature abhors self-fertilisation," and his more 

 precise statement, that, "No plant is perpetually self -fertil- 

 ised ; " and this view has been upheld by Hildebrand, Delpino, 

 and other botanists.^ 



Self- Fertilisation of Flowers. 



But all this time we have been only looking at one side of 

 the question, for there exists an abundance of facts which 

 seem to implj^ just as surely, the utter uselessness of cross- 

 fertilisation. Let us, then, see what these facts are before pro- 

 ceeding further. 



1. An immense variety of plants are habitually self-fer-( 

 tilised, and their numbers probably far exceed those which 

 are habitually cross-fertilised by insects. Almost all the very 

 small or obscure flowered plants Avith hermaphi'odite flowers 

 are of this kind. Most of these, however, may be insect 

 fertilised occasionally, and may, therefore, come under the rule 

 that no species are perpetually self-fertilised. 



2. There are many plants, however, in which special 

 arrangements exist to secure self-fertilisation. Sometimes the 

 corolla closes and brings the anthers and stigma into contact ; 

 in others the anthers cluster round the stigmas, both maturing 

 together, as in many buttercujjs, stitchwort (Stellaria media), 



^ See H. Miiller's Fertilisation of Flotoers, p. 18, 



y 



