HOW PLANTS GIVE OFF WATER 99 
sunflowers, etc., and take some leaves of geranium or 
other plants. Divide them into two lots, having in the 
lots an equal number of the various kinds. Immerse 
one lot in boiling water for a few moments to kill the 
plants. Immerse the other lot in cool water, in order 
to have the living plants also wet at the beginning of 
the experiment. Spread both lots out on a table to 
dry. In twenty-four hours examine them. Those 
which were killed have lost much more water than 
the living plants. Some of them may be dried so that 
they are crisp. The living plants are enabled to retard 
the loss of water, so that the process of evaporation is 
hindered, not only by the action of the hfe substance 
within the plant, but also by a regulating apparatus 
of the leaves. The loss of water from plants under 
these conditions we call transpiration. 
Does transpiration take place equally on both surfaces 
of the leaf? This can be shown very prettily by using 
the cobalt chloride paper. Since this paper can be 
kept from year to 
year and used re- >», Moly 
peatedly, it is a 
very simple mat- y 
ter to make these 3 és 
experiments. Pro- SASS dS 
vide two pieces of 
. Fig. 134. The holes (stomates) in the leaf bordered 
glass (d iscarded ~ by the guard cells. 
