plants that were set in the sunny window moisture will be seen
collecting on the inner surface of the tumbler. Where does this come
from? It is absorbed from the soil by the roots and is sent with its
load of dissolved plant food up through the stems to the leaves.
There most of the water is passed from the leaves to the air and is
condensed on the sides of the glass. A work of leaves then is to throw
off or to transpire moisture and thus make room for a new supply of
food-laden moisture. This water is thrown off through little pores or
mouths or stomata which are very small and very numerous on the under
side of the leaf. It will be noticed that the plant not placed in the
sunlight transpires very little moisture, showing that sunlight helps
the leaves in this work of transpiration.

How much water does a plant transpire or throw off from its leaves?

=Experiment.=--(See Fig. 60). Fill a common quart fruit jar or can
with soil and plant in it a kernel of corn, a bean, a cotton seed or
seed of some other plant. After the plant has grown to be twelve or
fifteen inches high, cut a piece of pasteboard a little larger than
the top of the jar, cut a hole in the centre as large as the stem of
the plant and make a slit from edge to centre. Soak the pasteboard in
melted wax or paraffine candle. Cool it and then place it over the
jar, slipping it around the plant stem. Now solder the pasteboard to
the jar with melted candle making the joints tight all the way around.
Then close up the slit and the hole about the stem. The jar is now
completely sealed and there is no way for water to escape except
through the plant. The plant should be well watered before the jar is
closed. Now weigh the jar and set in the sunlight. Weigh again the
next day. The difference in the two weights will represent the amount
of water transpired by the plant. The weighings may be repeated until