22 



GROWTH 



For prolonged experiments the use of self-registering auxanometers is 

 advisable. An instrument of this kind was first employed by Sachs 1 , who 

 allowed the end of the pointer in Fig. 7 to write upon a smoked cylinder 

 which made one revolution per hour. In the improved forms used by 

 Wiesner, Baranetzky, and other authors 2 , the growth was magni fied by an 

 axle and wheel arrangement. Other forms of magnifying levers have 

 been used for the registration of growth in thickness. 



The apparatus shown in Fig. 8 is the model constructed by Pfeffer on 

 Baranetzky 's principle. The cylinder / is covered with smoked paper, and makes 

 a partial revolution at given intervals of time, according to how the clock is set. 



A staircase curve is formed in which the 

 heights of the steps give the increments 

 of growth magnified by the ratio between 

 the radii of w and r. 



If the cylinder rotates continuously 

 at one revolution per hour, the vertical 

 distance between successive lines gives 

 the hourly amount of growth magnified 

 (Fig. 9). The cylinder may also make 

 one rotation per day when growth is slow, 

 and the curve may be directly traced on 

 squared paper by means of a pen carrying 

 ink made of aniline-blue and glycerine 3 . 

 A quite satisfactory instrument may easily 

 be constructed by allowing a smoked lamp 

 chimney to be rotated by the minute or 

 finger hand of an ordinary spring clock 

 on which it has been accurately centred. 

 A light straw may serve as the magnify- 



weTht 9 ' 



?en 



writing n cylinder; ^ = P isin g 



ing lever, a pin thrust through the end 

 of the long arm tracing the growth-curve. 



By using electrical transmission, the plant and registering apparatus may 

 be placed almost any distance apart (Frost, 1. c.). Whenever the growth-move- 

 ment is transmitted by means of threads, the length of these may be affected by 

 changes of temperature and of the percentage of moisture in the air 4 . Platinum 

 threads are unaffected by moisture, and have a low coefficient of expansion for 



1 Sachs, Arbeit, d. Bot. Inst. in Wiirzburg, 1872, Bd. I, p. 113. 



3 Wiesner, Flora, 1876, p. 466; Baranetzky, Die tagliche Periodicitat des Langenwachsthums, 

 1879, p. 21 ; Cohn, Jahresb. d. schles. Ges. f. vaterl. Cultur, 1879 ; Pfeflfer, Pflanzenphysiologie, 1881, 

 II, p. 86 ; Bot. Ztg., 1887, p. 29. On the registration of growth in thickness cf. Macmillan, American 

 Naturalist, May 1891 ; Reuss, Forstl. naturw. Zeitschrift, 1893, p. 146 ; Bot. Centralbl., 1893, Bd. LV, 

 p. 348 ; Frost, Minnesota Bot. Studies, 1894, IV, p. 181 ; Golden, Bot. Centralbl., 1894, Bd - LIX > P- 16 9 5 

 Baranetzky, Ber. d. Bot. Ges., 1899, p. 20. On the methods employed in Animal Physiology cf. 

 Langendorff, Physiol. Graphik, 1891 ; Marey, Methode graphique, 1878. 



8 For other forms of pen cf. Langendorff, 1. c., p. 44. 4 Cf. Sachs, Flora, 1876, p. 108 seq. 



