material is to preserve these mate- 
rials and render them available to 
the plant. 
A False Notion 
It is commonly supposed that the 
addition of humus to the soil tends 
to make it acid, because there is a 
certain amount of fermentation in 
decomposition. But this is true only 
when unnatural methods are used. 
The addition of quantities of fresh 
barnyard manure or the turning un- 
der of green crops produces acidity. 
But the natural decomposition of 
organic matter on the surface or 
mixed with the top soil, where suf- 
ficient air is present, will not pro- 
duce acidity. Many people suppose 
that those who have an acid _ con- 
dition of the stomach should not use 
acid fruits. The fact is that many of 
the acid fruits are the best cure for 
acidity, since the acid they contain 
is not the same as stomach acid, but 
another kind which helps to counter- 
act the acid of the stomach. The 
acid commonly found in acid soil is 
not the same seats acid produced 
O71 oe 
