they are made. | which plants |
| | obtain them. |
-------------------+---------------------+----------------+
Cellulose or | | |
woody fibre | Carbon | Air |
Starch |---------------------+----------------+
Sugar | | |
Gum | Oxygen | Water |
Fat and Oil | Hydrogen | |
-------------------+---------------------+----------------+
| Carbon | Air |
+---------------------+----------------+
Albuminoids | Oxygen | Water |
| Hydrogen | |
+---------------------+----------------+
| _Nitrogen_ | |
| Sulphur | |
| Phosphorus | |
-------------------+---------------------| Soil +
| _Phosphorus_ | |
| _Potassium_ | |
Ashes | _Calcium_ | |
| Magnesium | |
| Iron | |
-------------------+---------------------+----------------+
Water | Oxygen | Soil |
| Hydrogen | |
-----------------------------------------+----------------+

Here is a brief description of these chemical elements.

Oxygen, a colorless gas, forms one-fifth of the air.

Hydrogen, a colorless gas, forms a part of water.

Carbon, a dark solid, forms nearly one-half of all organic matter;
charcoal is one of its forms. The lead in your pencil is another
example.

Nitrogen, a colorless gas, forms four-fifths of the air. Found in all
albuminoids.

Sulphur, a yellow solid.

Phosphorus, a yellowish white solid.

Potassium, a silver white solid.

Calcium, a yellowish solid. Found in limestone.

Magnesium, a silver white solid.

Iron, a silver gray solid.

Of these elements the nitrogen, sulphur, phosphorus, potassium,
calcium, magnesium, and iron must not only exist in the soil but must
also be there in such form that the plant can use them.