Identifier: textbookofbotany00sach (find matches)
Title: Text-book of botany, morphological and physiological
Year: 1875 (1870s)
Authors: Sachs, Julius, 1832-1897 Bennett, Alfred W. (Alfred William), 1833-1902 Thiselton-Dyer, William T. (William Turner), 1843-1928
Subjects: Botany
Publisher: Oxford, Clarendon Press

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
e ofexactness by simple measurement with a measuring-rod. But for the purpose of moreexact observations it is more convenient to make use of smaller plants which do notgrow so rapidly, the growth during an hour not amounting to more than a millimetre, oreven less. In such cases a simple measuring-rod is not sufficiently exact; and I haveemployed in its place three different methods. In each of them a thin but strong threadof silk is fixed to the upper end of the stem or internode of the plant growing in apot, the thread passing vertically over an easily moveable pulley and moving an indexfixed to the free end of the thread or to the pulley. DAILY PERIODICITY OF GROWTH IN LENGTH. 7A7 I. The Thread-indicator is a simple contrivance in which the free end of the threadwhich hangs down from the pulley and is kept tight by a weight of a few grammes,carries a horizontal needle which moves freely over a graduated scale as the end of thethread which is fixed to the plant rises with its growth.
Text Appearing After Image:
Fig. 451.—Autographic Auxanometer, fof recofding- the development during short periods of an internode of a growingplant y,- ss the lines scored by the index z on the blackened paper / fixed to the cylinder C which is made to rotateeccentrically by means of the clock-work D. 2. In the Arc-indicator the thread cf(¥\g. 450) fixed to the plant a is carried overthe pulley d and fixed to a pin which is attached to a second pulley g. An index z madeof a straight and firm straw is fastened to this second pulley in the radial direction, its 74B MECHAXICAL LAWS OF GROWTH, free end pointing to a graduated scale on the arc of a circle m n. The equilibrium of theindex is secured by the small weight / which tends to turn the pulley in the oppositedirection with a force which keeps the thread cfva a state of tension. As the internodebelow the hook h lengthens, the weight / sinks, and a piece of the thread cf of equallength is rolled off the pulley^, thus raising the index on the arc. If the inde

Note About Images