48 AN ACCOUNT OF BRITISH FLIES. 



genus Aristolochia being cultivated in England, and one, A. clematis^ 

 which is a European species, has been found occasionally wild, 

 but is not an indigenous form. Few plants outside the Orchidacex 

 have become so modified for fertilization by insects as the one in 

 question. The flowers are all brownish-green, contrary to what we 

 should expect, as we are told in Darwin's " Origin of Species " " that 

 flowers have been rendered conspicuous in contrast with the green 

 leaves and in consequence at the same time beautiful, so that they 

 may be easily observed by insects." And likewise that *' if insects 

 had not been developed on the face of the earth, our plants would 

 not have been decked with beautiful flowers." 



In this Aristolochia we have a decidedly inconspicuous flower, not 

 only visited by insects, but having assumed most curious adaptations 

 to ensure fertilization. It is strange that this family, which calls in 

 the aid of insects more than most plants, should not have developed 

 a more conspicuously coloured blossom to attract them during the 

 time it has been forming those complicated habits and structures 

 relating to fertilization ! 



Each of these greenish blossoms commences with an expanded lip. 

 This passes into a funnel or throat (A), which is lined by hairs, so 

 placed that they allow the entrance of an insect, but not its exit. 

 This long funnel opens into a flask-shaped enlargement (B), in which 

 are placed the generative organs. This cavity is also lined by hairs, 

 especially at the base, around the anthers. The stigmas (?) are 

 placed above the anthers {$), and curve over them, the anthers 

 being surrounded by the hairs of the flask. 



Fertilization takes place in the following way : The Cecidomyia 

 enters the throat and passes down it, the hairs being placed so 

 as to allow its free passage. As soon as it enters the flask it crawls 

 about until its back, which is laden with pollen, comes in contact 

 with the stigma, and thus fertilizes them ; upon this taking place 

 they spring up and assume an erect position. At the same time 

 the hairs of the flask collapse and the anthers dehisce. The insect 

 then crawling down, gets the pollen upon its back. While all this has 

 been taking place the hairs of the funnel have withered up, and the 

 Cecid or other insect, laden with fresh pollen, flies away to another 

 blossom to repeat its experiences. But this is not all ; as soon as the 

 insects are free from the fertilized flower, the lip of the corolla 

 bends over the entrance to the blossom, and thus effectually stops 

 another fly from entering on a useless mission. The whole pedicel 

 assumes a bent appearance, while the unfertilized ones are erect. 

 This is, perhaps, one of the most curious adaptations that a plant 





