
98 {HE WORK OF PLANTS 
that the moisture of the air is often sufficient to redden 
the paper. 
Take two bell jars, as shown in Fig. 133. In one 
jar place a potted plant, the pot and earth being 
covered as described on page 96. Or cover the 
plant with a glass Jar. Pin to a stake in the pot a 
piece of the dried cobalt paper, and at the same time ~ 
pin to a stake, in another jar covering no plant, 
another piece of cobalt paper. They should be dried 
and entirely blue when they are put into the jars, and 
both should be put under the jars at the same time. 
In a few moments the paper in the jar with the plant 
will begin to redden. In a short time, ten or filteen 
minutes, probably, it will be entirely red, while the 
paper under the other jar will remain blue, or be only 
slightly reddened. The water vapour passing off from 
the living plant comes in contact with the sensitive cobalt 
chloride in the paper and reddens it before there is 
sufficient vapour present to condense as a film of morsture 
on the surface of the jar. 
The loss of water from plants. This is similar to 
evaporation, except that from a given area of leat 
surface less water evaporates than from an equal area 
ot water surface. It further differs from evaporation 
in that the living plant is enabled to retard or hold 
back the loss of water. This may be shown in the 
following way. Pull up several seedlings of beans, 
ee 
