236 TROPICAL NATURE, AND OTHER ESSAYS. 



situated on the equator off the west coast of South 

 America, and with a tolerably luxuriant vegetation in 

 the damp mountain zone, yet produce hardly a single 

 conspicuously-coloured flower ; and this is correlated 

 with, and no doubt dependent on, an extreme poverty of 

 insect life, not one bee and only a single butterfly having 

 been found there. 



Again, there is reason to believe that some portion of 

 the large size and corresponding showiness of tropical 

 flowers is due to their being fertilized by very large 

 insects and even by birds. Tropical sphinx-moths often 

 have their probosces nine or ten inches long, and 

 we find flowers whose tubes or spurs reach about the 

 same length ; while the giant bees, and the numerous 

 flower-sucking birds, aid in the fertilization of flowers 

 whose corollas or stamens are proportionately large. 



Recent Views as to Direct Action of Light on the 

 Colours of Flowers and Fruits. The theory that the 

 brilliant colours of flowers and fruits is due to the 

 direct action of light, has been supported by a recent 

 writer by examples taken from the arctic instead of from 

 the tropical flora. In the arctic regions vegetation is 

 excessively rapid during the short summer, and this is 

 held to be due to the continuous action of light through- 

 out the long summer days. " The further we advance 

 towards the north the more the leaves of plants increase 

 in size as if to absorb a greater proportion of the solar 

 rays. M. Grisebach says, that during a journey in 

 Norway he observed that the majority of deciduous trees 

 had already, at the 60th degree of latitude, larger leaves 

 than in Germany, while M. Ch. Martins has made a 

 similar observation as regards the leguminous plants 



