SIR J. C. BOSE, _Assisted by_ GURUPRASANNA DAS, L.M.S. In discussing the difficulties connected with investigations relating to longitudinal growth and its variations, special stress must be laid on the importance of maintaining external conditions absolutely constant. This constancy can only be maintained in practice for a short time. Lengthy periods of observation, moreover, introduce the uncertainty of complication arising from spontaneous variation of growth. The possibility of accurate investigation, therefore lies in reducing the period of the experiment to a few minutes during which we have to determine the normal rate of growth and its variation under a given changed condition. This would necessitate the devising of a method of very high magnification for record of the rate of growth.[S] [S] A short account of my researches with the High Magnification Crescograph has been published in the _Proceedings_ of the Royal Society. I shall in the following Papers give a detailed account of my investigations on growth and on allied phenomena. With auxanometers now in use, which give a magnification of about twenty times, it takes nearly four hours to determine the influence of changed condition in inducing variation of growth. It will be seen that if we succeeded in enhancing magnification from twenty to ten thousand times, the necessary period for experiment would be reduced from four hours to thirty seconds. The importance of securing a magnification of this order is sufficiently obvious. The problem of high magnification was first solved by my Optical Lever.[T] The tip of the growing organ was attached to the short arm of a lever, the axis of which carried a small mirror; in this way it was possible to obtain a magnification of a thousand times. The magnified movement of growth was followed with a pen on a revolving drum. The record laboured under the disadvantage of not being automatic. This defect was overcome by the use of the photographic method which however entailed the inconvenience and discomfort of a dark room. [T] BOSE--“Plant Response,” p 412. I have, for the past six years, been working with a different method, which has now been brought to a great state of perfection. The problem to be solved was the devising of a direct method of high magnification and the automatic record of the magnified rate of growth. METHOD OF HIGH MAGNIFICATION. The magnification in my Crescograph is obtained by a compound system of two levers. The growing plant is attached to the short arm of a lever, the long arm of which is attached to the short arm of the second lever. If the magnification by the first lever be _m_, and that by the second, _n_, the resulting magnification would be _mn_.