34 



IPOMOEA PURPUEEA. 



CHAP. II 



whilst the two tallest self-fertilised plants were only 15 and 

 12-5 inches in height, or as 100 to 59. 



I likewise sowed at the same time two lots of the same seeds 

 in a part of the garden which was shady and covered with 

 weeds. The crossed seedlings from the first looked the most 

 hsalthy, but they twined up a stick only to a height of 7i inches ; 

 whilst the self-fertilised were not able to twine at all ; and the 

 tallest of them was only 3 inches in height. 



Lastly, two lots of the same seeds were sown in the midst of 

 a bed of candy-tuft (Iberis) growing vigorously. The seedlings 

 came up, but all the self-fertilised ones soon died excepting one, 

 which never twined and grew to a height of only 4 inches. 

 Many of the crossed seedlings, on the other hand, survived; 

 and some twined up the stems of the Iberis to the height of 

 11 inches. These cases prove that the crossed seedlings 

 have an immense advantage over the self-fertilised, both when 

 growing isolated under very unfavourable conditions, and when 

 put into competition with each other or with other plants, as 

 would happen in a state of nature. 



Crossed and self-ftrtilised Plants of the Fourth Generation. Seed- 

 lings raised as before from the crossed and self-fertilised plants 

 of the third generation in Table III., gave results as follows : 

 TABLE V. (Fourth Generation.) 



Here the average height of the seven crossed plants is 69 -78 

 inches, and that of the seven self-fertilised plants 60 ' 14 ; or as 

 100 to 86. This smaller difference relatively to that in the 

 former generations, may be attributed to the plants having been 

 raised during the depth of winter, and consequently to their not 



