Such an enormous magnification cannot be employed in ordinary investigations on growth, for the moving spot of light indicating rate of growth, passes like a flash across the screen. But it is of signal service in my investigations 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 normal rate of growth. THE DEMONSTRATION CRESCOGRAPH. Before proceeding with accounts of further investigations, 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 reflected 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 magnification was far too great for use with quick growing plants like _Kysoor_. I, therefore, employed the slower growing flower bud of _Crinum_. It will be seen from Table X that the normal rate of growth of the lily is of the order of 0.0006 mm. per second. The normal excursion of the spot of light reflected from the Crescograph exhibiting growth was found to be 3 metres in five seconds or 60 cm. per second. This is a million times the actual rate of growth of the _Crinum_ bud. As it is easy to measure 5 mm. in the scale, it will be seen that with the Demonstration Crescograph it is possible to detect the growth of a plant for a period shorter than a hundredth part of a second.