PLANT NUTRITION. 17 
and sulphur. The latter comprise salts of soda, silica, 
manganese, together with chlorine and occasionally other 
ingredients. 
Of the salts just mentioned, the nitrates are of extreme 
.. Importance, inasmuch as nitrogen is an essential con- 
stituent of protoplasm—without nitrogen there can be 
no protoplasm, without protoplasm there can be no plant. 
The nitrogen is supplied to the plants from the soil in 
.. the form either of nitrates (potassic nitrate, sodic nitrate), 
or of ammonia salts in which the nitrogen is in combina- 
tion with hydrogen. The ammonia in the soil is made 
to combine with oxygen, and thus to form nitric acid, 
through the agency of minute organisms called ‘‘ Bac- 
teria,” which, like the yeast fungus, act as ferments ; and 
by their agency itis, as Mr. Warington has pointed out, 
in confirmation of the researches of Schlesing and 
Muniz, that the ammonia salts, which themselves are 
inert, or it may be harmful, get converted into useful 
nitrates. Ammonia salts applied to some soils do no 
good, because the needful germs or ferment bodies are 
not present in the soil; but where they do exist, they 
convert the useless into the uscful, as before said. These 
bacteria occur in all fermenting material, such as farm- 
yard dung, whose value as manure is in part accounted 
for by their presence and agency. It is probable in the 
future that just as the brewer uses his yeast to secure the 
conversion of starch into sugar, and the chemist ‘‘seeds” 
his solutions to effect the changes he wishes to bring 
about, and just as the gardener sows the spawn or germs 
of mushrooms in his mushroom bed, and obtains thereby 
a crop of succulent fungi, so the farmer may be able to 
apply to the soil the ferment-producing germs needed to 
change its quality, and render it available for plant food. 
When we have arrived at that point, manuring will be 
reduced to a science, and a pinch of the right material 
will be as efficient as a tom of our present compounds, 
