CHAP. VII. TABLE B. 283 



thirty-seven species in which the mean of the mean 

 heights of the crossed plants exceeds that of the self- 

 fertilised by twenty-two per cent. ; whereas there are 

 only five species in which the mean of the mean heights 

 of the self-fertilised plants exceeds that of the crossed, 

 and this only by nine per cent. 



The truth of the conclusion that the good effects of 

 a cross depend on the plants having been subjected 

 to different conditions or to their belonging to differ- 

 ent varieties, in both of which cases they would almost 

 certainly differ somewhat in constitution is supported 

 by a comparison of the Tables A and C. The latter 

 table gives the results of crossing plants with a fresh 

 stock or with a distinct variety ; and the superiority of 

 the crossed offspring over the self-fertilised is here 

 much more general and much more strongly marked 

 than in Table A, in which plants of the same stock 

 were crossed. We have just seen that the mean of the 

 mean heights of the crossed plants of the whole fifty- 

 four species in Table A is to that of the self-fertilised 

 plants as 100 to 87 ; whereas the mean of the mean 

 heights of the plants crossed by a fresh stock is to that 

 of the self-fertilised in Table C as 100 to 74. So that 

 the crossed plants beat the self-fertilised plants by 

 thirteen per cent, in Table A, and by twenty-six per 

 cent., or double as much, in Table C, which includes 

 the results of a cross by a fresh stock. 



TABLE B. 



A few words must be added on the weights of 

 the crossed plants of the same stock, in comparison 

 with the self-fertilised. Eleven cases are given in 

 Table B, relating to eight species. The number of 

 plants which were weighed is shown in the two left 

 columns, and their relative weights in the right 



