274 THE STRUCTURE OF FLOWERS. 



wasting it in the production of a great deal more pollen than 

 is usually required. 



An interesting experiment of Mr Darwin's proves this. 

 He placed a very small mass of pollen-grains on one side of 

 the large stigma of Ipomcea purpurea, and a great mass of 

 pollen over the whole surface of the stigmas of other flowers, 

 and the result was that the flowers fertilised with little 

 pollen yielded rather more capsules and seeds than did those 

 fertilised with an excess.* That normally intercrossing 

 flowers produce a great snperfluity of pollen is well known. 

 Thus Kolreuter found that sixty grains were necessary to 

 fertilise all the ovules of a flower of Hibiscus, while he cal- 

 culated that 4863 grains were produced by a single flower, or 

 eighty-one times too many.f Mr. Darwin says, "In order 

 to compensate the loss of pollen in so many ways, the anthers 

 produce a far larger amount than is necessary for the fer- 

 tilisation of the same flower ; . . . and it is still more plainly 

 shown by the astonishingly small quantity produced by 

 cleistogene flowers, which lose none of their pollen, in com- 

 parison with that produced by the open flowers borne by the 

 same plants ; and yet this small quantity suffices for the 

 fertilisation of all their numerous seeds." 



Mr. Darwin observed that when flowers were artificially 

 self-fertilised for several successive generations, a degeneracy 

 sometimes took place in the anthers and pollen ; and he seems 

 to attribute this to what he called the " evil effects " of self- 

 fertilisation ; but from the above-mentioned facts, which 

 occur so abundantly in nature, I am inclined to regard it as 

 an experimental verification and illustration of a universal 

 principle in nature, namely the preservation of energy 

 wherever possible, and that such cases as appeared under his 



• Cross and Self Fertilisation of Plants, p. 2S. 

 t Ibid., pp. 376, 377. 



