INSECTS AND FLOWERS 241 



has, however, been observed in the case of the common 

 fig (JFHcus caiica) that eggs of Blast ophaga gi*ossorum 

 laid in ordinary female flowers do not come to maturity, 

 or, in other words, that a normal female flower is 

 not converted into a gall, even if the wasp in question 

 sinks its ovipositor into it and deposits an egg in the 

 interior. For the style of the normal female flower of 

 Ficus carica is so long relatively to the ovipositor of 

 Blastophaga grossorum that the egg cannot be inserted 

 quite into the ovary, but is left at a spot which is not 

 favourable to its further development, and there perishes. 

 The gall- flowers of this species of fig, with their short 

 styles, are, on the other hand, pre-eminently adapted to 

 the reception of the egg at the spot where the ovule would 

 otherwise develop, while at the same time they are not 

 adapted to the production of seeds capable of germination, 

 since no pollen-tubes can develop upon their abortive 

 stigmas. Evidently we have here a case of complementary 

 functions or division of labour in accordance with the 

 following plan. The wasps which deposit their eggs in 

 the figs carry the pollen both to the short- styled gall- 

 flowers and to the long-styled ordinary female flowers, 

 and attempt to lay their eggs in both kinds of flower. 

 The gall-flowers are prepared expressly for the reception 

 of the wasps' eggs, and young wasps actually develop 

 in them ; but their stigmas not being adapted to the 

 reception of pollen, they do not promote the growth of 

 pollen-tubes, and no fertile seeds are produced. On the 

 other hand, pollen-tubes develop on the stigmas of the 

 long-styled flowers, and the latter produce fertile seeds; 

 but the long style prevents the proper placing of the 

 wasps' eggs, and consequently galls are never or very 

 seldom produced in connection with these flowers." 



The phenomenon of cross-pollination by insects is 



Q 



