Researches on growth and movement in plants by means of the high magnification crescograph

The auxanometers usually employed for recording longitudinal growth allow a magnification of only 10 or 20 times. The growth of a plant is, however, so slow that it requires several hours to detect the normal rate of growth and its variation under any changed condition. It is, moreover, impossible to maintain the external conditions absolutely constant throughout the experiment; even if this were possible, there would be some autonomous variation of the rate of growth during such lengthy periods. Hence, there must always be some uncertainty in the results obtained by a method which requires long time for observation. The elements of uncertainty can only be eliminated by reducing the period of the experiment to a few minutes, but that would necessitate devising a method of very high magnification and automatic record of the magnified rate of growth. I attempted to solve this problem by the employment of the optic lever, where an axis carrying a mirror underwent rotation proportional to the growth-elongation. The reflected spot of light magnified the movement of growth from 1000 to 10,000 times. The vertical movement of the spot of light was converted into a horizontal movement by means of a mirror suitably inclined. The excursion of the spot of light was followed by means of a pen on a drum revolving at a known rate; or the record was obtained automatically by photography. Hence a curve was obtained whose ordinate gave growth-movement, and abcissa time.