Researches on Growth of Plants

Abstract

I.—The High Magnification Crescograph. INVESTIGATION on growth is a matter of much practical importance, since the world's food supply is intimately dependent upon vegetative growth. The movements of stems, leaves, and roots under the action of various forces, such as light, warmth, and gravity, are often due to minute variations in the rate of growth. The discovery of laws relating to the movement of growing organs thus depends on the accurate measurement of normal growth and its changes. The great difficulty of the investigation arises from the extraordinary slowness of growth, the average value of which per second may be taken as 1/100000 in., or half the wave-length of sodium light. The “auxanometers” usually employed produce a magnification of about twenty times. Even here several hours must elapse before growth becomes perceptible, but during this long period the external conditions such as warmth and light would necessarily change, thus vitiating the results; moreover, autonomous variation of growth appears during lengthy periods. The elements of uncertainty can be removed only by reducing the period of experiment to a few minutes; but that would necessitate devising a method of very high magnification and the automatic record of the magnified rate of growth. I have been successful in this by my device of the High Magnification Crescograph, consisting of a system of two levers; the first magnifies a hundred times, and the second enlarges the first a hundredfold, the total magnification being 10,000 times. The various difficulties connected with the weight and friction at the bearing have been fully overcome.¹ The further difficulty in obtaining an accurate record of growth movement arising from friction of continuous corftact of the writing point was removed by an oscillating device by which the smoked glass plate moves to and fro at regular intervals of time, say one second (Fig. 1). The record consists of a series of dots, the distance between successive dots representing magnified growth during a second (Fig. 2a).