130 Darwin on the Effects of Cross- and Self- Fertilization. 



In Foxglove, — the flowers of which are naturally self-sterile 

 or nearly so, and in which crossing gave a marked advantage 



over self-fertilizing, both as to growth and productiveness, — a 

 decided, though small advantage, appeared to come from the 



In Origanum vulgare, crosses were made between different 

 plants of a large clump, long cultivated in a kitchen-garden, 

 which had evidently spread from a single root by stolons, 

 and which had become in a good degree sterile, as is usual 

 under such conditions. The crossing caused rather more seed 

 to form ; but the seedlings from the crossed did not surpass in 

 growth those of the self-fertilized ; " a cross of this kind did no 

 more good than crossing two flowers on the same plant of Lpo- 

 meea or Mimulus. Turned into the open ground, and both self- 

 and cross-fertilized the following summer, and equal pairs of 

 the resulting seeds planted on opposite sides of two very large 

 pots, the crossed plants from seed showed a clear superiority 

 over their self-fertilized brethren, at the rate of 100 to 80". 

 But this excess of height by no means gives a fair idea of the 

 vast superiority in vigor of the crossed over the self-fertilized 

 plants. The crossed flowered first and produced thirty flower- 

 stems, while the self-fertilized produced only fifteen, or half the 

 number. The pots were then bedded out, and the roots prob- 

 ably came out of the holes at the bottom, and thus aided their 

 growth. Early in the following summer, the superiority' of the 

 crossed plants, owing to their increase by stolons, over the self- 

 fertilized plants, was truly wonderful. . . . Both the crossed 

 and the self- fertilized plants being left freely exposed to the 

 visits of bees, manifestly produced much more seed than their 

 grandparents, — the plants of original clumps still growing close 

 by in the same garden, and equally left to the action of bees." 



These few cases must here suffice, and they give a fair gen- 

 eral idea of the main results reached, — somewhat qualified, 

 however, by certain instances iu which little or no benefit was 

 observed. Let it be remarked that while most of the cases 

 show decided and unequivocal good from the crossing, none 

 of them unequivocally tell to the contrary, as the advantage 

 appears sometimes in one direction, sometimes in another. 

 "Thus, the crossed and self- fertilized plants of Ipomcea, Puparer, 

 }{».-e<l.<i. odnruia. and Ltnuianthen were almost equally fertile, yet 

 the former exceeded" considerably in heighl 

 plants. On the other hand the cr> :ed plants 



of Mimuhu and Primula differed to an extreme degree in 

 fertility, but by no~means to a corresponding degree in height 



