274 SUMMARY OF MEASUREMENTS. CuAr. VII. 



cases in which the crossed plants were not taller than 

 the self-fertilised plants in any marked degree. 



(1.) Bianthus caryophyllus (third generation). This plant was 

 experimented on during four generations, in three of which the 

 crossed plants exceeded in height the self-fertilised generally by 

 much more than five per cent. ; and we have seen under Tablo 

 C that the offspring from the plants of the third self-fertilised 

 generation crossed by a fresh stock profited in height and fer- 

 tility to an extraordinary degree. But in this third generation 

 the crossed plants of the same stock were in height to the self- 

 fertilised only as 100 to 99, that is, they were practically equal. 

 Nevertheless, when the eight crossed and eight self-fertilised 

 plants were cut down and weighed, the former were to the latter 

 in weight as 100 to 49 ! There can therefore be not the least- 

 doubt that the crossed plants of this species are greatly superior 

 in vigour and luxuriance to the self-fertilised ; and what was the 

 cause of the self-fertilised plants of the third generation, though 

 so light and thin, growing up so as almost to equal the crossed 

 in height, I cannot explain. 



(2.) Lobelia fulgens (first generation). The crossed plants of 

 this generation were much inferior in height to the selfcfertilised, 

 in the proportion of 100 to 127. Although only two pairs were 

 measured, which is obviously much too few to be trusted, 

 yet from other evidence given under the head of this species, 

 it is certain that the self-fertilised plants were very much 

 more vigorous than the crossed. As I used pollen of unequal 

 maturity for crossing and self-fertilising the parent-plants, it is 

 possible that the great difference in the growth of their offspring 

 may have been due to this cause. In the next generation this 

 source of error was avoided, and many more plants were raised, 

 and now the average height of the twenty-three crossed plants 

 was to that of the twenty-three self-fertilised plants as 100 to 91. 

 We can therefore hardly doubt that a cross is beneficial to this 

 species. 



(3.) Petunia violacea (third generation"). Eight crossed plants 

 were to eight self-fertilised of the third generation in average 

 height as 100 to 131 ; and at an early age the crossed were 

 inferior even in a still higher degree. But it is a remarkable 

 fact that in one pot in which plants of both lois grew extremely 

 crowded, the crossed were thrice as tall as the self-fertilised. As 

 in the two preceding and two succeeding generations, as well aa 



