20 



GROWTH 



For exact determinations, direct optical measurements are preferable to 

 those made by attaching a thread to the growing apex, and magnifying the 

 amount of growth by passing the thread round the axis of a long balanced 

 pointer 1 (Fig. 7). The mere attachment of the thread and also the 

 tension exerted by it may suffice to influence the rapidity of growth. The 

 increase of the circumference by growth in thickness may be determined by 

 Hales* method, by passing a fine thread round the plant, one end of the 

 thread being fixed and the other attached to a magnifying lever 2 . Various 



FlG. 6. Horizontal microscope for 

 measuring growth. The coarse adjust- 

 ment is made by raising or lowering the 

 column s, the fine adjustment and also the 

 measurement of growth are made by 

 moving the graduated micrometer screw 

 m. A micrometer is also present in the 

 eye-piece and serves for still finer measure- 

 ments. /= focussing screw, / = spirit- 

 level, r = adjusting screws 3 . 



FlG. 7. Sachs 1 apparatus for measuring growth. One end of the 

 silk thread/" is attached to the plant, the other to the axis r of the 

 pointer s^ whose end moves downwards forty or eighty times the 

 amount that the stem elongates. The table / rests on non-vibrating 

 supports , and by means of the movable platform i the plant can 

 be placed at any desired height. A counterpoise is placed at k. 



forms of callipers and of micrometer screw gauges may be used to measure 

 the increase in diameter 4 . The latter may also be determined by observing 



1 Sachs, 1. c., and Text-book, 1875, p. 680. 



3 Hales, Statics, 1748, p. 74; Reinke, Bot. Ztg., 1876, pp. 114, 148. 



3 For the source of this and of the following apparatus see Bot. Ztg., 1887, p. 27. For similar 

 instruments cf. Wiesner, Zeitschr. f. Mikroskopie, 1893, Bd. X, p. 147, and Sachs, Arb. des Bot. Inst. in 

 Wiirzburg, 1878, Bd. n, p. 135. 



4 Kraus, Die Wasservertheilung in der Pflanze, 1879, I, p. 74 (Festschrift d. naturf. Ges. z. 

 Halle); Darwin and Bateson, Annals of Botany, Vol. VII, p. 468; 1890, Vol. IV, p. 118; 



