Page:Researches on Irritability of Plants.djvu/83

60 through the plant-chamber, at varying rates. A steady low temperature may thus be attained by adjusting the inflow of cooled air, the degree of cooling being dependent on the rate of flow. A thermometer placed inside the chamber indicates the temperature attained.

In order to raise the temperature of the plant-chamber an electrical device is employed. Inside the rectangular frame there is a coil of wire of German silver, the ends of the wire being led outside to two binding-screws. An electrical current from an outside battery is led through this wire, a variable resistance being also interposed in the circuit. The heat generated inside the chamber can be increased or decreased by changing the intensity of the current; this is accomplished by varying the adjustable resistance. In this manner it is quite easy to raise the temperature inside the plant-chamber to any degree that is desired, and to maintain it constant as long as necessary.

The temperature of the room, at the time of the experiment I am about to describe, was 27° C. I desired to take three records, differing from each other by intervals of 5° C. For this purpose I reduced the temperature of the plant-chamber to 22° C. and took the first record of the series. Next, by stopping the inflow of the cooled air and opening one of the side windows, I restored the temperature of the chamber to 27° C., and after allowing a suitable interval took the second record. Lastly, by means of the electrical heating device described, the temperature of the chamber was raised to 32° C. and the third record of