ELONGATION AND INTERNAL DIFFERENTIATION 



287 



weight, every elongation exhibited by the plant will cause a movement of the 

 pulley, which will be exaggerated by the pointer. This instrument does very 

 well if or lecture demonstration. The more elaborate auxanometers employed 

 in scientific research are constructed on the same principle, but are arranged 

 so as to record the amount of elongation automatically. In Fig. 84 we "have 

 again a pulley, serving the same purpose as in SACHS'S apparatus; it is, however, 

 connected with a larger pulley by means of which the movement is still further 

 exaggerated. Over the larger pulley runs a silk thread bearing at one end 

 a writing style, which registers the growth movements of the plant on a 

 blackened revolving cylinder. Registering auxanometers of this sort have 

 been designed by WIESNER (1876), BARANETZKY (1879), and PFEFFER 

 (1887). 



) PFEFFER 's auxanometer, as manu- 

 y Al.BRECHT of Tubingen. 



Fig. 83. Simple auxanometer. After DET- 

 MER (Smaller Practical Botany, Jena, 1903). 



If we have to deal, not with the total 

 growth of the plant, but with the distri- 

 bution of growth in it, and the amount 

 of growth in different zones, we must 

 measure, macro- or micro-scopically, seg- 

 ments mapped out by natural or artificial 

 marks (usually made with Indian ink), and 

 observe the distances these marks are apart at successive intervals of 

 time. 



We will now endeavour to make ourselves acquainted with the characteris- 

 tic features of growth in the root and shoot ; but we must take care to see 

 that in growth calculations all external factors, more especially temperature, 

 are kept as nearly as possible constant. We will begin with a study of growth 

 in the root, and in order to do this most conveniently we will cultivate the plant 

 in water. Should we desire to study its growth in natural surroundings we 

 employ boxes of sheet zinc filled with soil, but with one side replaced by a sloping 

 plate of glass. We allow the root to grow backwards along this plate and 

 observe it from without. SACHS (1873) marked off a zone just behind the 

 growing point on the main root of a seedling of Vicia faba by two fine lines of 



