12 



METHODS IN PLANT HISTOLOGY 



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 con- 

 nected with the regular outlets and should be on all the time. The 

 third bulb, which should be capable of raising the temperature 15° or 

 20° C, should be connected with a thermostat. An efficient thermo- 



FiG. 8. — Thermostat, heater, and switch of Land's electrical constant apparatus 



Stat, capable of keeping the variation in temperature within about 1° 

 can be made in a short time. Take a piece of soft steel f inch wide and 

 iV inch thick, and 17 inches long; lay upon it three strips of aluminum 

 of the same width and length, but only gV inch thick. These four pieces 

 are fastened together by drilling numerous holes, not more than j\ 

 inch in diameter, and riveting with pieces of brass wire. After fasten- 



