2* ON FLOWERS AND INSECTS. [LECT. 



An insect visiting a plant of the short-styled form 

 would dust its proboscis at a certain distance from the 

 extremity (Fig. 30, a), which, when the insect passed to 

 a long-styled flower, would come just opposite to the pis - 

 til (Fig. 29, st). At the same time, the stamens of this 

 second form (Fig. 29 a) would dust the proboscis at a 

 point considerably nearer to the extremity, which in 

 its turn would correspond to the position of the stigma 

 in the first form (Fig. 30, st). The two kinds of flowers 

 never grow together on the same stock, and the two 

 kinds of plants generally grow together in nearly equal 

 proportions. Owing to this arrangement, therefore, 

 insects can hardly fail to fertilise each flower with pollen 

 from a different stock. 



The two forms differ also in some other respects. In 

 the long-styled form, the stigma (st) is globular and 

 rough, while that of the short-styled is smoother, and 

 somewhat depressed. These differences, however, are 

 not sufficiently conspicuous to be shown in the figure. 

 Again, the pollen of the long-styled form is considerably 

 smaller than the other, a difference, the importance of 

 which is obvious, for each has to give rise to a tube 

 which penetrates the whole length of the style, from the 

 stigma to the base of the flower ; and the one has there- 

 fore to produce a tube nearly twice as long as that of 

 the other. The careful experiments made by Mr. Darwin 

 have shown that, to obtain the largest quantity of seed, 

 the flowers must be fertilised by pollen from the other 

 form. Nay, in some cases, the flowers produce more seed, 

 if fertilised by pollen from another species, than by 

 that from the other form of their own. 



This curious difference of the Primrose and Cowslip, 



