of light indicating rate of growth, passes like a flash
across the screen. But it is of signal service in my in-
vestigations on growth by the Method of Balance, to be
described in a future Paper. The principle of this method.
consists in making the Spot of light, which is moving in
response to growth, stationary, by subjecting the plant to a
compensating movement downwards. The slightest variation
caused by an external agent would make the Spot of light
move either to the right or to the left, according to the
stimulating or depressing character of the agent. It
will be understood, how extremely sensitive this method
is for detection of the most minute variation in the nor-
mal rate of growth.
THE DEMONSTRATION CRESCOGRAPH.
Before proceeding with accounts of further investiga- tions, I shall describe a form of Magnetic Crescograph with which I haVe been able to give' before a large audience demonstration of a striking character on various phenomena of growth. The magnification obtained was so great that I had to take some trouble in reducing it. This was accomplished by the. employment of a single, instead of a compound system of two levers. The re- flected spot of light was thrown on a screen placed at a distance of 4 metres, and this gave a magnification of a million times; it. is obvious that an increase of the distance of the screen to 8 metres would have given a magnification of 2 million times. As it was, even the loWer magnifica- tion was far too great for use with quick growing plants like [Cg/sour. I, therefore, employed the slower growing tlower bud -of Graham. lt will be seen from Table X that the normal rate of growth of the lily is of the order of 0-0000 mm. per second. The normal excursion of the spot of light reflected from the Crescograph exhibiting
