THE MEASUREMENT OF GROWTH 



21 



the movement of an attached metal point through a horizontal microscope, 

 when the other surface of the object is placed against an immovable 

 support. The growth in surface extent can be estimated in the same way 

 by noting the distances between originally equidistant marks placed on 

 the exterior of the object. 



The growth of curving objects may be accurately determined by this 

 last method, provided that the marks are placed at such distances that the 

 difference between the arcs and chords of the segments of circles between 



FIG. 8. Auxanometer for the automatic registration of growth. At regular intervals contact is made 

 in the clock () and the current operates an electro-magnetic arrangement at k, producing a partial 

 revolution of the cylinder (/). 



each pair can be neglected. The Indian ink marks are made by means of 

 a fine brush, or by the aid of a frame of parallel horsehairs, stretched over 

 a cork, or in the case of large objects by means of a toothed dividing wheel l . 



Jost, Ber. d. Bot. Ges., 1892, p. 600; Macmillan, American Naturalist, 1891 ; Frost, Minnesota Bot. 

 Studies, 1894, IV, p. 182 ; Golden, Bot. Centralbl., 1894, Bd. LIX, p. 169. The self-registering Zeiss 

 micrometer is one of the best instruments for slender stems and tendrils. Cf. Ewart, Ann. du Jard. hot. 

 de Buitenzorg, T. XV, 1898, p. 188. 



1 Hales, 1. c., pp. 186, 193 ; Dnhamel, Naturgesch. d. Baume, 1765, Bd. II, p. 36; Colta, 

 Naturbeob. iiber die Bewegung d. Saftes, 1806, p. 64; Wiesner, Sitzungsb. der Wiener Akad., 1883, 

 Bd. LXXXVIII, Abth. I, pp. 453, 473, 474 ; Grisebach, Archiv f. Naturgesch., 1843, IX, Bd. i, p. 269. 

 On the use of curved protractors cf. Sachs, Arbeit, d. Bot. Inst. in Wiirzburg, 1873, Bd. I, p. 391. 



