Ontario Teachers' Manuals: Nature Study

by Ontario. Department of Education

5. Plants.—Our study of humus shows the value of vegetable matter in soil. Besides contributing to the soil, plants break up rocks with their roots and dissolve them with acid excretions. It is interesting to study how a bare rock becomes covered with soil. First come the lichens which need no soil; on the remains of these the mosses grow. The roots of mosses and lichens help to disintegrate the rock with their excretions, so that, with frost, heat, air, and rain to assist, there is a layer of soil gradually formed on which larger plants can live. A forest develops. The trees supply shade from the sun and shelter from the wind, thus retarding evaporation. The roots of the trees hold the soil from being washed away. The dead leaves and fallen stems provide humus, and, on account of the water-holding capacity of humus, the forest floor acts like a sponge, preventing floods in wet seasons and droughts in dry times.

6. Animals.—Pupils should make a list of all burrowing animals and look for examples. The work of the earthworms is especially interesting. By eating the soil, they improve its texture and expose it to the air. Their holes admit air and water to the soil. The worms also drag leaves, sticks, and grass into their holes and thus add to the humus.

Darwin estimated that the earthworms in England passed over ten tons of soil an acre through their bodies annually. This is left on the surface and makes a rich top-dressing.

TILLING THE SOIL

1. It makes the soil finer, thus increasing the surface for holding film water and enabling it to conduct more water by capillarity.

2. It saves water from evaporation. (See Experiments 7 and 8, Form III.)

3. It aerates the soil, enabling roots to thrive better.

4. It drains (hence warms) the soil, assuring more rapid growth.

5. It kills weeds.

A large part of the work with soils may be done in connection with the garden studies, though most of the above mentioned experiments may be tried in the school-room. In ungraded schools any of the experiments may be made instructive to all the Forms.