284 
THE LEAF 
which burst under pressure, allowing the water to exude. 
This process is known as guttation, and the drops so formed, 
as guttation drops. These are often seen in the morning 
on the ends of grass blades, and on the points of leaves that 
have serrate margins, like the strawberry. Guttation drops 
are sometimes absorbed by the plant and sometimes they 
evaporate, depending on the needs of the plant and the 
amount of moisture in the air, or, as we say, the degree of 
humidity. 
The amount of water that leaves a plant in a day by 
transpiration alone is very great. For example, a moderate¬ 
sized sunflower plant will give off a quart a day under 
ordinary conditions. 
LABORATORY WORK ON TRANSPIRATION 
Turn the under side of a geranium leaf or other large leaf so it lies 
against a cool window pane, holding it there in some way if necessary. 
After half an hour remove it and note the drops of moisture which 
resulted from transpiration. Try other leaves in the same way. 
Fasten a watch crystal to the under side of a leaf, using clips to hold 
it and vaseline to make the edges air tight. Do the same with the 
upper side of another leaf. Which side gives off moisture as shown by 
drops on the watch crystal? Plunge a large leaf into water and set 
in the sun. On which side do bubbles appear? Wait half an hour. 
What kind of gas do they contain? What process in the leaf pro¬ 
duced them ? If you cannot answer this now, try again after review¬ 
ing photosynthesis. 
Take three leaves from the same plant. Coat one on both sides with 
paraffine or vaseline, one on the upper side only and one on the lower 
side only. Lay them aside till your next laboratory period. Describe 
all three. Which is least wilted? Why? Lay them all aside till all 
are wilted, observing them now and then and making a record of what 
happens. 
Hold a leaf up to the light and notice the arrangement of the veins 
and the soft parts. 
Thoroughly water a fern or other plant growing in a jar. Cover 
the earth with tinfoil, oilcloth, or paraffine to prevent evaporation 
from the surface. Weigh it carefully, then let it stand on the scales, 
