Chap. XVll. EVIL FROM INTERBREEDING. 109 



of the crossed plants grew from the first more quickly than the 

 opposed self-fertilised plants ; the sixth, however, was weakly and 

 was for a time beaten, but at last its sounder constitution jirevailed 

 and it shot ahead of its antagonist. As soon as each crossed plant 

 reached the top of its seven-foot rod its fellow was measured, and 

 the result was that, when the crossed plants were seven feet high 

 the self- fertilised had attained the average height of only five feet 

 four and a half inches. The crossed plants flowered a little before, 

 and more profusely than the self-fertilised plants. On opposite 

 sides of another small pot a large number of crossed and self- 

 fertilised seeds were sown, so that they had to struggle for bare 

 existence ; a single rod was given to each lot : here again the crossed 

 plants showed from the first their advantage ; they never quite 

 reached the summit of the seven-foot rod, but relatively to the 

 self- fertilised plants their average height was as seven feet to five 

 feet two inches. The experiment was repeated during several 

 succeeding generations, treated in exactly the same manner, and 

 with nearly the same result. In the second generation, the crossed 

 plants, which were again crossed, produced 121 seed - capsules, 

 whilst the self- fertilised, again self-fertilised, produced only 84 

 capsules. 



Some flowers of the Mimuhis Intevs were fertilised with their 

 own pollen, and others were crossed with pollen from distinct plants 

 gTOwing in the same pot. The seeds were thickly sown on 

 opposite sides of a pot. The seedlings were at first equal in 

 height; but when the young crossed plants were half an inch, 

 the self-fertilised plants were only a quarter of an inch high. 

 But this degree of inequality did not last, for, when the crossed 

 plants were four and a half inches high, the self-fertilised were 

 three inches, and they retained the same relative difference till 

 their growth was complete. The crossed plants looked far more 

 vigorous than the uncrossed, and flowered before them ; they 

 produced also a far greater number of capsules. As in the former 

 case, the experiment was repeated during several succeeding gene- 

 rations. Had I not watched these plants of Mimulus and Ipomoea 

 during their whole growth, I could not have believed it possible, 

 that a difference apparently so slight as that of the pollen being taken 

 from the same flower, or from a distinct plant growing in the same 

 pot, could have made so wonderful a difference in the gi'owth and 

 vigour of the plants thus produced. This, under a physiological 

 point of view, is a most remarkable phenomenon. 



With respect to the benefit derived from crossing distinct 

 varieties, plenty of evidence has been published. Sageret^^ re- 

 peatedly speaks in strong terms of the vigour of melons raised by 

 crossing different varieties, and adds that they are more easily 

 fertilised than common melons^ and produce numerous good seed. 



*' • Memoire sur les Cucurbitacees,' pp. 36, 28, 30. 



27 



