CH. IV] EMULSION EXPERIMENT. 91 



Whatever the explanation may be, it is interesting to note 

 that a shoot which has been rendered flaccid, by being cut 

 in the air and allowed to partially wither, can be rapidly 

 restored to turgescence by forcing water into its vessels 

 under pressure 1 . The cut end of such a withered shoot is 

 attached by a rubber tube to the short arm of a U tube 

 containing water. The position of the end of the shoot, 

 which droops flaccidly over, is noted on a vertical scale, 

 and mercury is poured into the long arm. Under the 

 pressure of about 10 cm. mercury, the plant recovers and 

 the end of the shoot can be traced with the naked eye 

 rapidly travelling up the scale. 



(105) Sacks' emulsion experiment 2 . 



To illustrate the fact that the pits of coniferous wood 

 are closed and that the water-current must therefore 

 filter through them, the following experiment is useful. 



Prepare an emulsion of vermilion by adding a few 

 paint-brushes full of good colour to a beaker of water, and 

 filtering it through coarse filter-paper. Take a piece of 

 yew 6 or 7 cm. in length and attach it by a rubber tube 

 to the lower end of a glass tube a meter in length held 

 vertically in a clamp. Fill the tube with emulsion and 

 observe that colourless water drips from the lower end of 

 the wood. After an hour or so remove the wood : note 

 the red colour of the young wood due to injection of the 

 cut tracheids with vermilion. Cut a shaving off the 

 surface to show that the colour only extends to a small 

 depth. 



1 Sachs, Text-book of Botany, Edition n. p. 683. 



2 Sachs' Arbeiten, n. p. 299. 



