204 TRANSPIRATION. 



tubing with water, and (holding the wood vertical) raise 

 the tubing and note the appearance of water on the upper 

 surface as soon as the water-level in the tube equals that 

 of the upper end of the wood. 



(c) The pressure required to force water through the 

 wood in different directions may be applied by means of 

 a column of water in a long straight tube, or by mercury 

 in a J-tube. G-et three cylinders of Pine wood of the same 

 dimensions say, 5 cm. long and 2 cm. in diameter but 

 cut in different planes, so that one is longitudinal, the 

 second radial, the third tangential ; a turner will prepare 

 cylinders like this very cheaply, and they must then be 

 soaked well in water. Experiment with each cylinder in 

 turn as follows. 



Join the cylinder by rubber tubing to a vertical glass 

 tube about 1 metre long (or use several shorter pieces 

 joined up by rubber tubing, if a long enough tube is not 

 available), join a funnel to the upper end of the tube, and 

 support the funnel in a retort- stand on a shelf. Place a 

 clip on the rubber tubing just above the wood cylinder, 

 and set below the latter a graduated vessel to catch the 

 water that passes through the wood. Pour clean water 

 into the funnel until the whole apparatus is filled, then 

 release the clip and note how long it takes for, say, 100 c.c. 

 to pass through. 



(d) If in an experiment like the preceding we use an 

 emulsion i.e. water containing fine insoluble particles in 

 suspension we shall be able to determine that the pits in 

 the tracheids of Coniferous wood are closed, hence the 

 water of the transpiration current must filter through 

 them ; and that vessels are, on the other hand, continuous 

 tubes, though of limited length. 



Prepare longitudinal cylinders of Pine wood (A) and of 

 the wood of a Dicotyledonous tree (.#) ; in each case com- 

 pare cylinders of different lengths e.g. 2 cm., 10 cm., 

 20 cm. Soak the cylinders in water. Stir some vermilion or 

 cinnabar into distilled water, and filter it through blotting- 

 paper ; examine a drop of the filtrate with the microscope, 

 and note the numerous suspended particles in it. Force 



