presently be shown that in plants immersed in water-bath
growth is often found to persist even up to 5730.
The only way of removing the complication arising from thermal radiation lies in varying the temperature condition of the plant, by direct contact with water at different tem- peratures. This procedure will also remove uncertainty regarding the body of the plant assuming the temperature of surrounding non-conducting air. The disturbing effect of sudden variation of temperature is also obviated by a more uniform regulation otf rise of temperature. The inner cylinder containing the plant is filled with water; heat from gradually warmed water in the outer cylinder is conducted across the inner cylinder made of thin copper and raises the tcmpe 'ature. of the water contained in the inner cylinder with great uniformity. A clock-hand goes round once in a minute; the experimenter, keeping his hand on the stop- cock, adjusts the rate of rise of water in the inner cylin- der, so that there is a rise, say, of one-tenth of a degree every ti seconds or of one degree every minute. The mass of water acts as a governor, and prevents any sudden fluctuations of temperature. The adoption of this parti- cular device eliminated the erratic changes in the rate of growth that had hitherto proved so battling.
The elongation recorded by the Crescograph will now be made up of (1‘) physical expansion, (2) expansion brought about by absorption of water, and (3) the pure acceleration of growth. The. disentanglemeut of these different elements presented many difficulties. I was, however, able to find out the relative values of the first two factors in reference to the elongation of growth. This was done, by carrying out a preliminary experiment with a specimen of plant in which growth had been Completed. It was raised through 20°C in temperature, records being taken both at the beginning and at the end. This was for obtaining a measure of the
