PLANTS AND ANIMALS 37 
walls of plants consist of a wood substance called cellu- 
lose. In green and growing plants this cellulose is thin 
and tender, but as the plant matures it becomes hard and 
woody. The work of building the plant is done within 
the cells. 
3. Formation of plant compounds.—Certain soluble 
compounds are carried from the soil into plants through 
the roots and deposited in the cells. These are met by 
carbon, brought into the plant through the leaves. These 
substances supply the building materials for the manu- 
facture of plant compounds. The master builder is 
protoplasm, tucked away in the cells. No one knows 
just what protoplasm is, but it represents life, without 
which there could be no growth. Every live, active cell 
contains protoplasm, the life principle. Herein is con- 
tained the vital spark that makes all growth possible. 
The various agricultural elements used by plants or animals are: 
O, Oxygen. P, Phosphorus. 
H, Hydrogen. K, Potassium. 
N, Nitrogen. Mg, Magnesium. 
C, Carbon. M, Manganese. 
Cl, Chlorine. Fe, Iron. 
Na, Sodium. Si, Silicon. 
S, Sulphur. Ca, Calcium. 
4, Starch—When the soluble 
soil material or plant food has 
been carried up through the 
long channel of cells and reaches 
the leaves, it is brought in con- 
tact with the carbon dioxide that i a. teen 
has been pulled into the leaf cells sion Bey tibet Tee 
through the little mouths on the 
undersides of the leaves. Here these various compounds 
are upset and disintegrated through the action of heat, 
sunlight, protoplasm and chlorophyll, with the result that 
STARCH CELLS 
