12 
METHODS IN PLANT HISTOLOGY 
this thermostat is given in the Botanical Gazette for November, 1911. 
One familiar with tools and electricity could make this thermostat 
at a very moderate outlay. Unless the coil in the heater is perfectly 
protected, there will be a short circuit. This danger can be obviated, 
in large measure, by using oil instead of water in the jacket. 
Fig. 10.—Thermostat, heater, and switch of Land’s electrical constant apparatus 
Another form of heater, using long electric bulbs instead of a 
coil, can be made with less skill. From a sheet of transite f inch thick, 
make a box just the size of the bottom of the bath and about 4 inches 
deep. In this box put three long electric bulbs. Two of the bulbs, 
about 250 watt, giving a temperature of about 40° C., should be 
connected with the regular outlets and should be on all the time. 
