LABORATORY NOTE AN APPARATUS FOR THE MEASUREMENT OF STEM ELONGATION BY C. HUNTER AND E. M. RICH

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1 44 C. HUNTER AND E. M. RICH (22) SACHS. Ueber den Einfliiss des Tageslichts auf Neubildiing und Entfaltung verschiedener Pflanzenorganen. Bol. Zeil Gesa»inielle Ahhandlungen, 1. pp Leipzig, (23) SnivE, J. W. A Study of Physiological Balance in Nutrient Media. Physiohigical Researches. 1, pp (24) TEODORESCO, M. K. C. Action indirecte de la lumi&re sur la tige et les feuilles. Rev. gen. de Bol. 2, p (25) WEBER. Ueber den Eintiuss farbigen Liclites auf die Assimilation und die damit zusammenhangende Vermehrung der Aschenbestandtheile in Erbsenkeimlingen. Laiidw. Versuchs-Statioiieii. 18, p (26) WiESNER, J. Formanderungen von Pflanzen bei Kultur ini absolut feuchten Kaunie und in Dunkeln. Bey. der deuucji. Hot. des. 9, PP- 4'' LABORATORY NOTE AN APPARATUS FOR THE MEASUREMENT OF STEM ELONGATION BY C. HUNTER AND E. M. RICH T N the eourse of an investigation recently earried out in this department it became necessary to compare the rates of elongation of the stem of Impatiens Balsamina during relatively short intervals of time. The horizontal microscope proved to be unsuitable for this purpose and tht' various forms of au.xanometer were found to be insuffieiently sensitive. E\'entually a satisfactory apparatus was devised whieh, it is thought, may be of use in laboratory practice. The lower end of a piece of glass tubing (C) 5-7 mm. in length, drawn out as fine as possible, and sealed off in a flame, rests in the axil of a small leaf in close pro.ximity to the growing point. C is maintained in a vertical position by means of a glass tube (T) of slightly larger diameter which is attached to the edge of a microscope slide by means of Canada Balsam. The upper end of C bears a square horizontal platform of miea (M) whose side is 0-5 cm. On the upper surface oi M a small flat pii-ee of platinum foil (E) is fixed with shellae. A fine insulated copper wire is in contact with the platinum foil and is connected at its other end to a resistance {R). This is connected through a galvanometer (G) with a battery of dry cells (B), and to a spherometer (S) rigidly clamped above the plant and adjusted so that its central point is immediately above the platinum electrode II. The atta( hment CME can slide freely iu 7", and, consequently, as

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3 46 C. HUNTER AND E. M. RICH the stem elongates the platinum electrode " is raised the corresponding height. The spherometer is adjusted so that contact is just made between its central point and K this is indicated by the deflection of the needle of the galvanometer owing to the completion of the circuit. The reading of the spherometer and the time are noted. The circuit is then broken by withdrawing the centre point of the spherometer a fraction of a millimetre this distance is duly recorded.. 2izn ELONGATION OF C, riay I3'J 1922; ll-^5ani - Ii «3LI 2.4 XI JO TI nc observation kept on the galvanometer and the time noted when the circuit is completed again owing to the raising of the electrode due to the growth of the stem. The operation is then repeated and thus the rate of growth of the stem can be aecurately determined. The spherometer employed was graded into O-(K)5 mm. units, but even smaller distances than these might be measured by suitable vernier attachments. Corrections due to the interfering effects of fluctuations in temperature on the metal supports and on the glass

4 Laboratory Note 47 tnbc C (luring the course of the experiment can be applied. The platform CME must be constructed so as to be as light as possible in order that no nndne strain is made on the plant. It was found possible to construct a platform with a weight of gm. which caused no injury to the plant. The order of the results obtainable by means of this apparatus is indicated by the accompanying graph. Obviously the apparatus can only be employed with plants similar to Impatiens where the lower end of C can be inserted in the axil of a leaf close to the growing point. A lamp, or other indicator, to show when the circuit is completed, can be substituted for the galvanometer, but the latter was found to give the best results. Thanks are due to Mr H. E. George of the Department of Physics, who has assisted in devising this apparatus. HiATT BAKER LABORATORY, DEPARTMENT OF BOTANY, UNIVERSITY OF BRISTOL. December, i\)zz. FORTHCOMING MEETING OE THE BRITISH ASSOCIATION, 1923, AT LIVERPOOL PROVISIONAL ARRANGEMENTS FOR SECTION K A T the forthcoming meeting of the British Association for the \ Advancement of Science at Liverpool (September 12-19) ^^^^ Botanical Section will be presided over by Mr A. G. Tansley, F.R.S. The programme promises to be an interesting one, and it is hoped to make it representative of the chief branches of Botany. In recent years joint discussions between two Sections have been a feature of these gatherings, and at Liverpool it is expected that a discussion on "Virus Diseases" will be arranged with eithtr the Section of Physiology or Agriculture. Much important work of grt'at biological interest has recently been done upon these strange maladies, and a stock-taking of present views upon them is considered to be opportune. Plant physiology will again occupy a prominent ))lace in the programme, and contributions have already been promised by Dr F. F. Blackman and by Prof. V. H. Blackman. Tlu' latter will

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