i.] THE PRIMROSE AND COWSLIP. 29 



a point considerably nearer to the extremity, which in 

 its turn would correspond to the position of the stigma 

 in the first form (Fig. 32, 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, in- 

 sects can hardly fail to fertilize 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 fertilized by pollen from the other 

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

 if fertilized by pollen from another species, than by that 

 from the other form of their own. 



This curious difference in the Primrose and Cowslip, 

 between flowers of the same species, which Mr. Darwin 

 has proposed to call Dimorphism, is found in most 

 species of the genus Primula, but not in all. 



The Cowslip and Primrose resemble one another in 

 many respects, but the honey they secrete must be very 

 different, for while the Cowslip is habitually visited 



