168 PINOT's experiment. [CH. VII 



base of the root should be kept damp by a strip of filter- 

 paper hanging over the seed like a rider and dipping into 

 the water below. 



(199) Pinot's experiment^. 



This experiment is the same in principle as the last, 

 but the resistance is supplied by the descent of the root 

 into mercury. The arrangement of the experiment is 

 shown in Sachs' paper on the growth of roots l A shallow 

 dish of 6 — 8 cm. in diameter is filled with mercury to a 

 depth of 2 — 3 cm., on which is a layer of water 5 — 6 mm. 

 in thickness. A split cork is firmly jammed like a rider 

 on the edge of the dish, and to it a bean is pinned so that 

 the root lies horizontally in the water just touching the 

 surface of the mercury. The whole arrangement is 

 covered with a bell-jar and left for 24 — 48 hours. Another 

 way of fixing the bean, which we find convenient, is 

 simply to support the pin, on which the cotyledons are 

 impaled, in a clamp attached to a small heavy stand. 

 We usually keep the cotyledons wet with a strip of filter- 

 paper dipping into the water. 



(200) Knight's experiment^. 



Sachs figures^ an apparatus which any one can con- 

 struct for himself, and by which it may be demonstrated 



^ Ann. Set. Nat., series 1, T. xvii. 1829 (Bibliography, p. 94). See 

 also Hofmeister in Pringsheim's Jahrbilcher, Vol. iii. p. 105. 



2 Arbeiten, i. p. 452, fig. 14. 



3 Phil. Trans. 1806. 



^ Physiologic (French Trans. ), p. 124. 



