1 Ocr., 1899.] QUEENSLAND AGRICULTURAL JOURNAL. 377 
HOW PLANTS FEED. 
In order to know how plants feed, it is advisable in the first place to see 
What a plant is made of. If a plant is burnt,it will be noticed that a 
considerable portion, which varies from 92 to as highas 993 per cent. of the 
total weight of the plant, passes off in the form of an invisible gas, and that the 
balance remains as an incombustible ash. The portion that is lost constituted 
what is known as the organic part of the plant as distinct from the ash or 
inorganic constituent. Plants feed by means of their leaves and roots, the 
caves supplying the greater portion of the organic constituents, whereas the 
roots supply the inorganic. 
Plants consist of three main parts—roots, branches, and leaves. ‘The 
leaves are the lungs of the plant, and have on their under surface innumerable 
small openings or mouths, which are open during the day and closed at night, 
and through which the plant breathes, and i€ is Y means of these mouths 
that plants obtain direct from the atmosphere the whole of the carbon required 
to build up the tissue of the plant, and to form the various carbo-hydrates, such 
as starch, sugar, &e. In the atmosphere there ig al 
in 10,000 of a heavy gas, known as carbon di-oxide, w 
of carbon and 2 parts of oxygen, and this 
plant through the mouths, and the plant has the ower of breaking it up into 
its component parts. The carbon it retains an assimilates, converting it, in 
conjunction with water, first into cellulose, and a p : i 
xygen it 
returns to the atmosphere. Small as the percentage of carbon di-oxide in the 
air appears to be, it is nevertheless several times greater than that required by 
any crop, and, although it is always being used during daylight by all plants, 
there is no diminution in the amount, as the supply is being constantly renewed 
by means of fires of all kinds, and by the exhalations of 
; L . all animals. Plants 
are distinguished from animals by this means, as plants inhale carbon di-oxide 
and exhale oxygen, and animals inhale oxygen and exhale carbon di-oxide, and 
thus the amount of carbon di-oxide in the atmosphere remains stable. N itrogen, 
though it constitutes about four-fifths of the atmosphere, cannot in most 
cases be obtained by plants directly from this 
3 d : Source, though leguminous 
plants have a power to assimilate nitrogen, probably from the air that is 
contained in the water that is taken up by the plant by means of its roots. 
Jt is their power of assimilating nitrogen that renders certain varieties of 
leguminous plants, such as vetches and cow peas, of such value for green-crop 
manuring, as it is the cheapest way of supplying a soil with nitrogen, and, where 
the soil is deficient in organic matter as well, itis one of the cheapest and most 
effective methods of manuring. ‘The oxygen and 
1 : hydrogen required by the 
plant are obtained from the water that is taken up by 
4 the roots, and which is 
absolutely necessary for the plant’s existence, and all the other 
enter into the composition of the plant are obtained in 
dissolved in the water that is taken up by the roots, 
matter can be taken up by the roots—everything must be 
Water alone is often unable to dissolve thé ingredient 
which are present in the soil in an insoluble form, but water containing air and 
carbon di-oxide acts on the insoluble matter present in the soil, and slowly 
renders the insoluble matter soluble, and so available for plant food. Stagnant 
power has not this power; hence one of the great advantages of draining soils, 
which I alluded to when writing on drainage in the Queensland Agricultural 
Journai for September, 1897, is plainly shown—namely, that the aération of the 
soil which follows the remoyal of the stagnant water assists disintegration, as it 
supplies the necessary air and earbon di-oxide to the water, to enable it to act on 
the insoluble matter of the soil, and render it soluble and available for plant 
food. 
elements that 
a soluble form that is 
No insoluble or solid 
in solution in water. 
8 required by plants, and 
PLANT FOODS. 
Having shown how plants feed, the next thing to be considered is what 
foods are essential to the proper development of plants. In describing what a 
plant is made of, I have already stated that it consists of organic and inorganic 
