CH. IV] EMULSION EXPERIMENT. 83 



(105) Sachs' emulsion experiment^ 



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 vermillion 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 3 or 4 inches in length and attach it by a rubber 

 tube to the lower end of a glass tube 3 feet 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 vermillion. Cut a shaving off the 

 surface to show that the colour only extends to a small 

 depth. 



An interesting modification of the experiment is to 

 plunge the cut ends of transpiring branches into emulsion : 

 in this way the distribution of the transpiration cun-ent 

 in the cross section may be studied in various plants. 

 Diluted skim milk stained black with osmic acid makes 

 a good emulsion. 



(106) Injection of vessels' 



Cut two similar branches of Portugal laurel, place one 

 in water, the other in melted cocoa-butter, into which it 

 must dip as deeply as the vessel allows. After an hour, 

 during which the cocoa-butter is kept melted, take the 



1 Arbeiten, ii. p. 299. 



2 Elfving, Bot. Zeitung, 1882. 



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