72 THE METHOD OF DARWIN. 



He covered the plants with nets, and cross- 

 and self-fertilized them artificially without cas- 

 tration, so as to make the cases parallel in all 

 respects. The seeds were thoroughly ripened; 

 the cross- and self-fertilized seeds were chosen 

 in pairs that had germinated simultaneously, 

 and were planted on opposite sides of the same 

 pot. When one of a pair t became sickly or 

 injured, both were thrown away. All the 

 seeds which remained after a number of pairs 

 were thus planted were sown and left to grow 

 up crowded on opposite sides of the same pot. 

 The soil was carefully made uniform ; the 

 plants on the two sides of a pot were always 

 watered at the same time and as equally as 

 possible. The plants on the two sides of a pot 

 were separated by a partition, but the pot was 

 turned so that the two sides would be equally 

 lighted. In this way the cross- and self-fer- 

 tilized seedlings that competed with each other 

 were subjected to as nearly similar conditions 

 as human ingenuity could produce. Different 

 sets of competing plants were subjected to 

 different conditions, to determine whether the 

 inequality between the cross- and self-fertilized 

 seedlings would show itself only under favor- 

 able, or unfavorable, or under all circumstances. 



In making the comparisons the eye alone 



