152 



PHASEOLUS MULTIFLORUS. 



CHAP. V. 



neous variability. But the above distance would be very far from 

 sufficient to prevent intercrossing : cabbages have been known to 

 cross at several times this distance ; and the careful Gartner* 

 gives many instances of plants growing at from 600 to 800 yards 

 apart fertilising one another. Professor Hoffmann even maintains 

 that the flowers of the kidney-bean are specially adapted for 

 self-fertilisation. He enclosed several flowers in bags ; and as 

 the buds often dropped off, he attributes the partial sterility of 

 these flowers to the injurious effects of the bags, and not to the 

 exclusion of insects. But the only safe method of experimenting 

 is to cover up a whole plant, which then never suffers. 



Self-fertilised seeds were obtained by moving up and down in 

 the same manner as bees do the wing-petals of flowers protected 

 by a net ; and crossed seeds were obtained by crossing two of the 

 plants under the same net. The seeds after germinating on sand 

 were planted on the opposite sides of two large pots, and equal- 

 sized sticks were given them to twine up. When 8 inches 

 in height, the plants on the two sides were equal. The crossed 

 plants flowered before the self-fertilised in both pots. As soon 

 as one of each pair had grown to the summit of its stick both 

 were measured. 



TABLE LIII. 

 Phaseolus multiflorus. 



The average height of the five crossed plants is 86 inches, and 

 chat of the five self-fertilised plants 82 35 ; or as 100 to 96. The 

 pots were kept in the greenhouse, and there was little or no 

 difference in the fertility of the two lots. Therefore as far as 

 these few observations serve, the advantage gained by a cross is 

 yery small. 



* 'Kenntniss der Befruchtuug,' 1844, pp. 573, 577. 



