Theory of Plant Breeding 



may be altered. New enzymes or other chemical sub- 

 stances will be formed, and others may be destroyed. 

 If in a desert plant, more material is used up in thicken- 

 ing the epidermis-walls of the leaves, then there is less 

 available for other purposes. 



If strong and vivid flower-colours are produced in the 

 clear atmosphere, and strong sunshine of an Alpine 

 meadow, then something different must be going on 

 in the wonderful chemical laboratory which we call a 

 flower-petal. 



Changes of this kind must surely influence the delicate 

 balance of supply and demand in the life of the plant, 

 and the proportions and nature of its various ferments 

 and enzymes. 



It is not necessary to call in any complex theory of 

 pangenesis for the inheritance of these ferments, for 

 enzymes or whatever goes to produce them are most 

 certainly inherited. 



Remembering this delicate balance in the physiologi- 

 cal life of a plant, the old views as to the importance of 

 changes in the outside world or environment become 

 much less difficult to maintain. Nor is it so impossible to 

 believe in the inheritance of the effects of use and disuse. 



There are such cases as the evolution of the American 

 trotting horse. In 1818 the record speed was i mile 

 in 3 minutes. In 1824 it was reduced to 2 minutes 

 34 seconds, in 1848 to 2 minutes 30 seconds, and so 

 on until in 1896 it was 2 minutes 10 seconds.-^ 



The rigorous selection of these animals for one quite 

 useless and artificial accomplishment is not at all more 

 severe than the usual struggle for life amongst seedlings. 



But that the continual practice of all the ancestry 

 since 18 18 has had no effect whatever in cutting down 

 the record seems a thoroughly artificial and unnatural 

 supposition. 



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