300 THE EFFECTS OF CROSSING CHAP. VIII. 



opponents, was well shown by their relative weights 

 when cut down, which was as 100 to 78. The mean 

 height of the flower-stems on the twenty-five inter- 

 crossed plants in the ten pots taken together, was to 

 that of the flower-stems on the twenty-five self-ferti- 

 lised plants, as 100 to 92. Thus the intercrossed 

 plants were certainly superior to the self-fertilised in 

 some degree ; but their superiority was small compared 

 with that of the offspring from a cross between distinct 

 plants over the self-fertilised, this being in the ratio 

 of 100 to 70 in height. Nor does this latter ratio 

 show at all fairly the great superiority of the plants 

 derived from a cross between distinct individuals over 

 the self-fertilised, as the former produced more than 

 twice as many flower-stems as the latter, and were 

 much less liable to premature death. 



(2.) Ipomceapurpurea. Thirty-one intercrossed plants 

 raised from a cross between flowers on the same plants 

 were grown in ten pots in competition with the same 

 number of self-fertilised plants, and the former were 

 to the latter in height as 100 to 105. So that the 

 self-fertilised plants were a little taller than the inter- 

 crossed ; and in eight out of the ten pots a self-fertilised 

 plant flowered before any one of the crossed plants in 

 the same pots. The plants which were not greatly 

 crowded in nine of the pots (and these offer the fairest 

 standard of comparison) were cut down and weighed ; 

 and the weight of the twenty-seven intercrossed plants 

 was to that of the twenty -seven self-fertilised as 100 

 to 124; so that by this test the superiority of the 

 self-fertilised was strongly marked. To this subject of 

 the superiority of the self-fertilised plants in certain 

 cases, I shall have to recur in a future chapter. If we 

 now turn to the offspring from a cross between 

 distinct plants when put into competition with self- 



