TRANSPIRATION. 203 



Repeat the experiment, colouring the cold water with 

 eosin, and note that in A the veins after a time become 

 tinged, while this does not happen in B. If the blocking 

 of the vessels in B cannot be seen clearly, use an ad- 

 ditional plant, and cut across the stem to see that the wax 

 has actually entered. 



Another plan is to use 20 per cent, gelatine which melts 

 in water at about 33 and stiffens in cold water at about 

 20 C. ; blacken the gelatine, by mixing it with Indian ink, 

 or colour it with eosin. 



267. Mobility of Water in Wood. It is interesting 

 to compare the ease with which water moves through the 

 wood of Coniferous and Dicotyledonous trees in different 

 directions. In experiments with longitudinal cylinders of 

 Coniferous wood, it is as well to close up the protoxylem 

 vessels by turning a knife-point in the pith so as to 

 form a small cavity at each end of the piece, and filling 

 up this cavity by applying a little melted shellac or other 

 cement. 



(a) From a Pine twig (Fir or Yew may be used) cut 

 pieces about 20 cm. long and 1 or 2 cm. diameter ; remove 

 the outer tissue from the wood, and smooth the cut ends 

 with a sharp knife. Place the pieces in water for an hour 

 to soak the wood, then remove one piece and wipe the 

 ends dry ; no water escapes, because that would require 

 the entrance of air, which does not readily pass through 

 wet membranes. Hold the piece vertically, and with a 

 brush place some water on the upper end; the drop 

 disappears, while a corresponding drop appears on the 

 lower end. Invert the piece, wipe dry, and repeat the 

 experiment. 



(6) That small pressure is sufficient to set in motion 

 the threads of water in the wood is also shown as follows. 

 Join a longitudinal Pine-wood cylinder by rubber tubing 

 to the shorter arm of a J-tube, and pour water in at the 

 other end ; water escapes from the upper cut surface until 

 the pressure is equalised. Another plan is to slip a long 

 piece of rubber tubing over one end of the wood, fill the 



