CHAP. VIII. ON SELF-FERTILISED PLANTS. 311 



of their flowers tended in some degree to change and to 

 become uniform. When no intercrossing with other 

 plants of the same stock was allowed, that is, when 

 the flowers were fertilised with their own pollen in 

 each generation their colour in the later generations 

 became as uniform as that of plants growing in a 

 state of nature, accompanied at least in one instance 

 by much uniformity in the height of the plants. But 

 in saying that the diversified tints of the flowers on 

 cultivated plants treated in the ordinary manner are 

 due to differences in the soil, climate, &c., to which 

 they are exposed, I do not wish to imply that such 

 variations are caused by these agencies in any more 

 direct manner than that in which the most diversified 

 illnesses, as colds, inflammation of the lungs or pleura, 

 rheumatism, &c., may be said to be caused by expo- 

 sure to cold. In both cases the constitution of the 

 being which is acted on is of pieponderant importance. 





