Mr. C. Darwin on the Fertilization of Papilionaceous Flowers. 459 



L. — On the Agency of Bees in the Fertilization of Papilionaceous 

 Flowers, and on the Crossing of Kidney Beans. Bv Charles 

 Darwin, F.R.S.* 



In a brief notice published by me on this subject last year, 

 I stated that bees always alight on the left wing-petal of the 

 Scarlet Kidney Bean, and in doing so depress it ; and this acts 

 on the tubular and spiral keel-petal, which causes the pistil 

 to protrude : on the pistil there is a brush of hairs ; and by the 

 repeated movement of the keel-petal the hairs brush the pollen 

 beyond the anthers on to the stigmatic surface. This complex 

 contrivance led me to suppose that bees were necessary to the 

 fertilization of the flower : accordingly I enclosed some few 

 flowers in bottles and under gauze ; and those which were not in 

 any way moved did not set a single pod, whereas some of those 

 which I moved in imitation of the bees produced fine pods. But 

 I then stated that the experiment was tried on much too small 

 a scale to be trusted. I have this year covered up between 3 

 and 4 feet in length of a row of Kidney Beans, just before the 

 flowers opened, in a tall bag of very thin net. Nothing in the 

 appearance of the plants would lead me to suppose that this was 

 in any way injurious to their fertilization : and I think this con- 

 clusion may be trusted ; for some of the flowers which I moved in 

 the same way as the bees do, produced pods quite as tine as 

 could be found in the uncovered rows. 



The result was that the covered-up plants had produced by 

 August 13th only thirty-five pods, and in no one case two pods 

 on the same stalk, whereas the adjoining uncovered rows were 

 crowded with clusters of pods. There were many flowers still on 

 the plants when uncovered ; and it was curious to see how, in a 

 few days afterwards, as soon as the bees had access to them, 

 a number of pods hanging in clusters of three and four together 

 were produced. On August 17th I again put the net on a later 

 crop. The covered plants now produced ninety- seven pods, borne 

 on seventy-four stalks, showing that the same stalk often pro- 

 duced more than one pod. This time I kept an equal length of 

 uncovered beans ungathercd ; and on this length there were 292 

 pods, or exactly thrice as many as on the covered plants. Taking 

 this number as the standard of comparison for the first experiment 

 (which, however, is hardly fair, as my gardener thinks the second 

 crop was more productive than the first), more than eight times 

 as many pods were produced on the uncovered than on the 

 covered rows. The Kidney Bean is largely frequented by the 

 Thrips -, and as I have with some other plants actually seen a 

 Thrips which was dusted with pollen leave several granules on the 



* Extracted iVom the ' Gardeners' Chronicle' of November 13, 1858. 



