278 SUMMAEY OF MEASUKEMENTS. CHAP. VII. 



insects and a few self-fertilised plants were grown on the opposite 

 Bides of four pots. They attained to a nearly equal height, the 

 crossed having a very slight advantage. 



(18.) Vandellia nummular! folia. Twenty crossed plants raised 

 from the seeds of perfect flowers were to twenty self-fertilised 

 plants, likewise raised from the seeds of perfect flowers, in height 

 as 100 to 99. The experiment was repeated, with the sole 

 difference that the plants were allowed to grow more crowded ; 

 and now the twenty-four tallest of the crossed plants were to 

 the twenty-four tallest self-fertilised plants in height as 100 to 

 94, and in weight as 100 to 97. Moreover, a larger number of the 

 crossed than of the self-fertilised plants grew to a moderate 

 height. The above-mentioned twenty crossed plants were also 

 grown in competition with twenty self-fertilised plants raised 

 from the closed or cleistogamic flowers, and their heights were as 

 100 to 94. Therefore had it not been for the first trial, in which 

 the crossed plants were to the self-fertilised in height only as 

 100 to 99, this species might have been classed with those in 

 which the crossed plants exceed the self-fertilised by above five 

 per cent. On the other hand, the crossed plants in the second 

 trial bore fewer capsules, and these contained fewer seeds, than 

 did the self- fertilised plants, all the capsules having been 

 produced by cleistogamic flowers. The whole case therefore must 

 be left doubtful. 



(19.) Pisum sativum (common pea). Four plants derived from 

 a cross between individuals of the same variety wore in height 

 to four self- fertilised plants belonging to the same variety as 100 

 to 115. Although this cross did no good, we have seen under 

 Table C that a cross between distinct varieties adds greatly to 

 the height and vigour of the offspring ; and it was there explained 

 that the fact of a cross between the individuals of the same variety 

 not being beneficial, is almost certainly due to their having been 

 self- fertilised for many generations, and in each generation 

 grown under nearly similar conditions. 



(20, 21, 22.) Canna warscewiczi. Plants belonging to three 

 generations were observed, and in all of three the crossed were 

 approximately equal to the self-fertilised ; the average height of 

 the thirty- four crossed plants being to that of the same number 

 of self-fertilised plants as 100 to 101. Therefore the crossed 

 plants had no advantage over the self-fertilised ; and it is pro- 

 bable that the same explanation here holds good as in the case 

 of Pisum sativum ; for the flowers of this Canna are perfectly 



