270 INFLUENCE OF CORRELATION AND EXTERNAL STIMULI 



rudimentary ; the stimulus exercised by the pollen-tube induces the further develop- 

 ment of the female sexual apparatus in these plants. That this stimulus has nothing 

 to do with the fertilizing influence of the pollen-tube is in the nature of the case 

 evident, and moreover it is exercised by foreign pollen in orchids which are incapable 

 of hybridization. 



The following observation of Treub 1 is of particular interest: Individuals of 

 Liparis latifolia have been found on which the ovary of closed flower-buds was 

 swollen up, and contained ovules just like those which would otherwise develop 

 only after pollination. No pollination had been effected, but the ovaries were 

 infested by small insect-larvae which had brought about the same effect as usually 

 follows the action of the pollen-tube. The pollen-tube in its growth abstracts from 

 the style and the ovary the material necessary for its elongation and therefore 

 determines a flow of plastic material to the ovary. The larvae had exactly the same 

 influence. Of similar nature, only less striking, is the well-known fact that apples and 

 pears which are inhabited by larvae ripen earlier than do others. The very 

 varied processes which are observed in the ripening of fructifications of lower and 

 higher plants evidently belong to the same category. 



1 Treub, L'action des lubes polliniques sur le developpement des ovules chez les Orchidees, in Ann. 

 du Jardin botanique de Buiten/org, iii. p. 122. 



