256 SUMMAKY OF MEASUREMENTS. CHAP. VII. 



with various surrounding species. The seeds sown at 

 the same time in a garden have generally been matured 

 during the same season and in the same place ; and in 

 this respect they differ much from the seeds sown by 

 the hand of nature. Some exotic plants are not 

 frequented by insects in their new home, and there- 

 fore are not intercrossed ; and this appears to be a 

 highly important factor in the individuals acquiring 

 uniformity of constitution. 



In my experiments the greatest care was taken that 

 in each generation all the crossed and self-fertilised 

 plants should be subjected to the same conditions. 

 Not that the conditions were absolutely the same, for 

 the more vigorous individuals will have robbed the 

 weaker ones of nutriment, and likewise of water when 

 the soil in the pots was becoming dry ; and both lots 

 at one end of the pot will have received a little more 

 light than those at the other end. In the successive 

 generations, the plants were subjected to somewhat 

 different conditions, for the seasons necessarily varied, 

 and they were sometimes raised at different periods of 

 the year. But as they were all kept under glass, they 

 were exposed to far less abrupt and great changes of 

 temperature and moisture than are plants growing out 

 of doors. With respect to the intercrossed plants, theii 

 first parents, which were not related, would almosl 

 certainly have differed somewhat in constitution ; and 

 such constitutional peculiarities would be variously 

 mingled in each succeeding intercrossed generation, 

 being sometimes augmented, but more commonly 

 neutralised in a greater or less degree, and sometimes 

 revived through reversion ; just as we know to be the 

 case with the external characters of crossed species and 

 varieties. With the plants which were self-fertilised 

 during the successive generations, this latter important 



