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 1 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 ro 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 1818 has had no effect whatever in cutting down 
the record seems a thoroughly artificial and unnatural 
supposition, 
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