18 GARDENING INDOORS AND UNDER GLASS 
cold, and hen, sheep, pigeon or other special man- 
ures are not safe in the hands of the beginner, as 
they are one-sided, being especially rich in nitrogen 
and likely either to burn the plants or to cause too 
soft and watery growth. 
This brings us to the point where it is necessary 
to say a few words about the theory of manures, 
for they are not all alike and what would be wise 
to give a plant under some circumstances under 
others would be quite wrong, just as you would not 
think of feeding beefsteak to a baby just recovering 
from the colic, while it might be a very good thing 
for a hungry man who was going to saw up your 
wood-pile. 
Plants of all sorts — in pots, in the garden or in 
a ten-acre lot —require three kinds of food ele- 
ments: nitrogen, phosphoric acid and _ potash. 
These elements may be fed to the plants in various 
forms; for instance, the nitrogen in hen manure, or 
in cottonseed meal, or in salts from the nitrate fields 
of Chile, known as nitrate of soda; the phosphoric 
acid from bone, or from acid phosphate (a ground 
rock treated with acid) ; the potash from wood ashes 
or from German potash salts (muriate or sulphate 
of potash). Plants, to do their best, require that 
all three elements shall be present in sufficient 
amounts to supply their wants. 
It is not necessary, however, to go very deeply 
into the science of plant foods in order to grow 
