58 IPOMCEA PURPUREA. Chap. II. 



always in some degree more productive than the self- 

 fertilised plants, by whatever standard they are com- 

 pared. The degree differs greatly; but this depends 

 chiefly on whether an average was taken of the seeds 

 alone, or of the capsules alone, or of both combined. 

 The relative superiority of the crossed plants is chiefly 

 due to their producing a much greater number of cap- 

 sules, and not to each capsule containing a larger 

 average number of seeds. For instance, in the third 

 generation the crossed and self-fertilised plants pro- 

 duced capsules in the ratio of 100 to 38, whilst the 

 seeds in the capsules on the crossed plants were to 

 those on the self-fertilised plants only as 100 to 94. 

 In the eighth generation the capsules on two self- 

 fertilised plants (not included in the above table), 

 grown in separate pots and thus not subjected to any 

 competition, yielded the large average of 5*1 seeds. 

 The smaller number of capsules produced by the self- 

 fertilised plants may be in part, but not altogether, 

 attributed to their lessened size or height ; this being 

 chiefly due to their lessened constitutional vigour, so 

 that they were not able to compete with the crossed 

 plants growing in the same pots. The seeds produced 

 by the crossed flowers on the crossed plants were not 

 always heavier than the self-fertilised seeds on the 

 self-fertilised plants. The lighter seeds, whether pro- 

 duced from crossed or self-fertilised flowers, generally 

 germinated before the heavier seeds. I may add that 

 the crossed plants, with very few exceptions, flowered 

 before their self-fertilised opponents, as might have 

 been expected from their greater height and vigour. 



The impaired fertility of the self-fertilised plants was 

 shown in another way, namely, by their anthers being 

 smaller than those in the flowers on the crossed plants. 

 This was first observed in the seventh generation, but 



