PART III. | THE MECHANISMS OF FLOWERS. 75 
opening of the anthers progresses slowly towards the centre of the 
flowers, and each stamen as it dehisces bends outwards and turns 
its pollen-covered side outwards. These stigmas are fully developed 
before the innermost stamens join the others, and the flowers, 
which before could only dust their visitors with pollen, can hence- 
forth be fertilised either with their own or other pollen. All 
visitors which alight, bearing pollen, in the middle of the flower 
effect cross-fertilisation ; others, which alight first on a petal and 
Fic. 25.—Ranunculus Flammula, L. 
1.—Flower just opening. 
2—Flower in which the stamens are fully developed, the stigma still immature. é 
3 —Esgential organs of a flower in which the stigmas are fully mature, and the anthers are not 
_ yet withered. 
a, immature anthers ; b, anthers about to dehisce ; c, ditto, dehisced ; d, ditto, empty ; e, carpel. 
touch the anthers and then the stigmas, can accomplish either self- 
fertilisation or cross-fertilisation. So if insects alight in equal 
numbers in the two ways, cross-fertilisation must be the more 
frequent result. After numerous observations on this and the 
following species of Ranunculus, I am able to state that the two 
modes of alighting are equally common for small insects; but all 
larger insects (which are about as long as the diameter of the 
flower) come in contact with the stigmas and the anthers at the 
