152 On F lowers and Insects. 



proportions. Owing to this arrangement, therefore, 

 insects can hardly fail to fertilise each flower with 

 pollen from a different stock. 



6. The two forms differ also in some other 

 respects. In the long-styled form, the stigma (si) is 

 globular and rough, while that of the short-styled 

 form is smoother and somewhat depressed. These 

 differences, however, are not sufficiently conspi- 

 cuous to be shown in the figure. Again, as 

 shown in the figure, the pollen of the long-styled 

 form 1 is smaller than the other, a difference the 

 importance of which is obvious, for each grain of 

 pollen sends out a tube which penetrates the 

 whole length of the style, from the stigma to the 

 base of the flower; and the one has therefore 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. 



7. This curious difference in the Primrose and 

 Cowslip, between flowers of the same species, 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 



