IMPORTANCE OF WATER TO PLANTS

We learned in a previous paragraph that plant roots take moisture from the soil.  What becomes of this moisture?  We will answer this question with an experiment.

=Experiment.=—­Take a pot or tumbler in which a young plant is growing, also a piece of pasteboard large enough to cover the top of the pot or tumbler; cut a slit from the edge to the centre of the board, then place it on top of the pot, letting the stem of the plant enter the slit.  Now close the slit with wax or tallow, making it perfectly tight about the stem.  If the plant is not too large invert a tumbler over it (Fig. 21), letting the edge of the tumbler rest on the pasteboard; if a tumbler is not large enough use a glass jar.  Place in a sunny window.  Moisture will be seen collecting on the inner surface of the glass.  Where does this come from?  It is absorbed from the soil by the roots of the plant and is sent with its load of dissolved plant food up through the stem to the leaves.  There most of the moisture is passed from the leaves to the air and some of it is condensed on the side of the glass.

By experiments at the Cornell University Agricultural Experiment Station, Ithaca, N.Y., it has been found that during the growth of a sixty bushel crop of corn the plants pump from the soil by means of their roots, and send into the air through their leaves over nine hundred tons of water.  A twenty-five bushel crop of wheat uses over five hundred tons of water in the same way.  This gives us some idea of the importance of water to the plant and the necessity of knowing something of the power of the soil to absorb and hold moisture for the use of the plant.  Also the importance of knowing if we can in any way control or influence the water-holding power of the soil for the good of the plant.

SOURCES OF SOIL WATER

From what sources does the soil receive water?  From the air above, in the form of rain, dew, hail and snow, falling on the surface, and from the lower soil.  This water enters the soil more or less rapidly.

ATTITUDE OF THE SOILS TOWARDS WATER

Which soils have the greater power to take in the rain which falls on their surface?

[Illustration:  FIG. 21.  To show what becomes of the water taken from the soil by roots.  Moisture, sent up from the roots, has been given off by the leaves and has condensed on the glass.]

[Illustration:  FIG. 22.—­PERCOLATION EXPERIMENT.  To show the relative powers of soils to take in water falling on the surface. A, sand; B, clay; C, humus; D, garden soil.]