302 THE EFFECTS OF CROSSING CHAP. VIII. 



raised by intercrossing flowers on these plants, which 

 strictly consisted of the same plant, and other seedlings 

 raised from self-fertilised flowers, were carefully com- 

 pared from thei < earliest youth to maturity ; and they 

 did not differ at all in height or in constitutional 

 vigour. Some flowers on these seedlings were then 

 crossed with pollen taken from a distinct seedling, and 

 other flowers were self-fertilised ; two fresh lots of 

 seedlings being thus raised, which were the grand- 

 children of the plant that had spread by stolons and 

 formed a large clump in my garden. These differed 

 much in height, the crossed plants being to the 

 self-fertilised as 100 to 86. They differed, also, to a 

 wonderful degree in constitutional vigour. The crossed 

 plants flowered first, and produced exactly twice as 

 many flower-stems ; and they afterwards increased by 

 stolons to such an extent as almost to overwhelm the 

 self-fertilised plants. 



Reviewing these five cases, we see that in four of 

 them, the effect of a cross between flowers on the same 

 plant (even on offsets of the same plant growing on 

 separate roots, as with the Pelargonium and Origa- 

 num) does not differ from that of the strictest self- 

 fertilisation. Indeed, in two of the cases the self-fer- 

 tilised plants were slightly superior to such intercrossed 

 plants. With Digitalis a cross between the flowers on 

 the same plant certainly did do some good, yet very 

 slight compared with that from a cross between distinct 

 plants. On the whole the results here arrived at, if 

 we bear in mind that the flower-buds are to a certain 

 extent distinct individuals and occasionally vary inde- 

 pendently of one another, agree well with our general 

 conclusion, that the advantages of a cross depend on 

 the progenitors of the crossed plants possessing some- 

 what different constitutions, either from having been 



