288 CONSTITUTIONAL VIGOUR CHAP. VIII 



After the germinating seedlings had been planted 

 in pairs on the opposite sides of several pots, the 

 remaining seeds, whether or not in a state of germina- 

 tion, were in most cases sown very thickly on the two 

 sides of an additional large pot ; so that the seedlings 

 came up extremely crowded, and were subjected to 

 extremely severe competition and unfavourable condi- 

 tions. In such cases the crossed plants almost invari- 

 ably showed a greater superiority over the self-fertilised, 

 than did the plants which grew in pairs in the pots. 



Sometimes crossed and self-fertilised seeds were 

 sown in separate rows in the open ground, which was 

 kept clear of weeds ; so that the seedlings were not 

 subjected to any competition with other kinds of 

 plants. Those however in each row had to struggle 

 with the adjoining ones in the same row. When fully 

 grown, several of the tallest plants in each row were 

 selected, measured, and compared. The result was 

 in several cases (but not so invariably as might have 

 been expected) that the crossed plants did not exceed 

 in height the self-fertilised in nearly so great a degree 

 as when grown in pairs in the pots. Thus with the 

 plants of Digitalis, which competed together in pots, the 

 crossed were to the self-fertilised in height as 100 to 

 70 ; whilst those which were grown separately were only 

 as 100 to 85. Nearly the same result was observed 

 with Brassica. With Nicotiana the crossed were to 

 the self-fertilised plants in height, when grown 

 extremely crowded together in pots, as 100 to 54; 

 when grown much less crowded in pots as 100 to 66, 

 and when grown in the open ground, so as to be sub- 

 jected to but little competition, as 100 to 72. On the 

 other hand with Zea, there was a greater difference in 

 height between the crossed and self-fertilised plants 

 growing out of doors, than between the pairs which 



