38 IPOMCEA PURPTJKEA CHAP. IL 



Each of these nine crossed plants is higher than its opponent, 

 though in one case only by three-quarters of an inch. Their 

 average height is 83 -94 inches, and that of the self-fertilised 

 plants 68-25, or as 100 to 81. These plants, after growing to 

 their full height, became very unhealthy and infested with 

 aphides, just when the seeds were setting, so that many of the 

 capsules failed, and nothing can be said on their relative 

 fertility. 



Crossed and self-fertilised Plants of the Eighth Generation. As 

 just stated, the plants of the last generation, from which the 

 present ones were raised, were very unhealthy and their seeds 

 of unusually small size ; and this probably accounts, through 

 abnormal premature growth, for the two lots behaving dif- 

 ferently to what they did in any of the previous or succeeding 

 generations. Many of the self- fertilised seeds germinated before 

 the crossed ones, and these were of course rejected. When the 

 crossed seedlings in Table IX. had grown to a height of between 

 I and 2 feet, they were all, or almost all, shorter than their self- 

 fertilised opponents, but were not then measured. When they 

 had acquired an average height of 32'28 inches, that of the 

 self-fertilised plants was 40 '68, or as 100 to 122. Moreover, 

 every one of the self-fertilised plants, with a single exception, 

 exceeded its crossed opponent. When, however, the crossed 

 plants had grown to an average height of 77 - 56 inches, they 

 just exceeded (viz., by 7 of an inch) the average height of the 

 self-fertilised plants; but two of the latter were still taller than 

 their crossed opponents. I was so much astonished at this whole 

 case, that I tied string to the summits of the rods ; the plants 

 being thus allowed to continue climbing upwards. When their 

 growth was complete they were untwined, stretched straight, 

 and measured. The crossed plants had now almost regained 

 their accustomed superiority, as may be seen in Table IX. 



The average height of the eight crossed plants is here 113 25 

 inches, and that of the self-fertilised plants 96 '65, or as 100 tc 

 85. Nevertheless two of the self-fertilised plants, as may be seen 

 in the table, were still higher than their crossed opponents. 

 The latter manifestly had much thicker stems and many more 

 lateral branches, and looked altogether more vigorous than the 

 self-fertilised plants, and generally flowered before them. The 

 earlier flowers produced by these self-fertilised plants did not 

 set any capsules, and their anthers contained only a small 

 amount of pollen ; but to this subject I shall return. Neverthe- 



