126 
FLORIDA STATE HORTICULTURAL SOCIETY. 
Plants derive their food from the air 
and the soil. The air supplies direct 
chiefly the element carbon, although it is 
the original source of hydrogen, oxygen 
and nitrogen. Hydrogen and oxygen are 
supplied mainly through the soil in the 
form of water. 
About 95 per cent, of the total dry 
matter of plants comes from the air; the 
remaining 5 per cent, is in the incombus¬ 
tible or ash constituents which are sup¬ 
plied exclusively by the soil. These ash 
constituents are indispensable for without 
them the carbon of the air, the hydrogen 
and oxygen of the water and the nitro¬ 
gen of the soil and air could not enter in¬ 
to plant life. 
The plant takes its food througii the 
leaves and roots which are called the or¬ 
gans of nutrition. 
The chlorophyll or green coloring mat¬ 
ter in the leaf-cell plays an important 
part for it is in these leaf-cells that the 
carbonic acid of the air is decomposed 
through the influence of light and heat, 
the carbon being retained while the oxy¬ 
gen is given off. This process is called 
assimilation and takes place during the 
daytime, while at night the food made 
during the day is changed, whereby it 
can be transferred in solution wherever it 
is needed. Iron as well as daylight is nec¬ 
essary in the formation of chlorophyll. 
The carbon absorbed by the plant and the 
hydrogen and oxygen taken up by the 
roots in the form of water meet in the 
leaves of the plant and are formed into 
starch, sugar, fat, etc., and the same ele¬ 
ments together with nitrogen and a little 
sulphur form the albuminoids. 
The manner in which the roots take up 
food 1 is very different from that of the 
leaves, for the surface membranes of the 
roots are not full of holes and solid mat¬ 
ter cannot pass through. Therefore, the 
food must be in solution and its absorp¬ 
tion by the rootlets is obtained by means 
of diffusion or “osmosis.” The food de¬ 
rived from the soil is not taken up as in¬ 
dividual chemical elements but chiefly in 
the form of acids or salts. Thus nitrogen 
is combined with oxygen to form nitric 
acid and when united with bases like po¬ 
tassium or calcium forms potassium ni¬ 
trate or calcium nitrate. These weak so¬ 
lutions taken up by the roots are concen¬ 
trated in the upper part of the plant ow¬ 
ing to rapid evaporation by the leaves 
and are used in the formation of new tis¬ 
sue. 
While considerable research has been 
given to the work of determining the 
functions performed by the different con¬ 
stituents taken into' the plant, yet there is 
very little definite knowledge on this 
subject at the present time. 
As the material furnished by the air is 
supplied freely and abundantly to' every 
plant it will not be necessary to devote 
any time to it but we will turn our atten¬ 
tion to the substances furnished by the 
soil. The soil does not always supply the 
plant with sufficient material for its 
growth and as these deficiencies must be 
made good by man before he can hope 
for abundant harvests we will consider 
for a few moments the part they play in 
plant life. 
Of the elements supplied by the soil as 
plant food, magnesium, iron and sulphur, 
and sometimes calcium, are usually found 
to exist in sufficient quantities to supply 
the requirements of plants. Potassium, 
phosphorus and nitrogen, and some- 
