Go to any piece of ground which is left wild and untouched you
will find it covered with grass weeds, and other plants; if you
dig up a small plot you will find innumerable tiny roots creeping
through the ground in every direction. Each of these roots has a
sponge-like mouth by which the plant takes up water. Now, imagine
rain-drops falling on this plot of ground and sinking into the
earth. On every side they will find rootlets thirsting to drink
them in, and they will be sucked up as if by tiny sponges, and
drawn into the plants, and up the stems to the leaves. Here, as
we shall see in Lecture VII., they are worked up into food for
the plant, and only if the leaf has more water than it needs,
some drops may escape at the tiny openings under the
leaf, and be drawn up again by the sun-waves as invisible vapour
into the air.
Again, much of the rain falls on hard rock and stone, where it
cannot sink in, and then it lies in pools till it is shaken apart
again into vapour and carried off in the air.
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