THE MOLECULAR FORCES IN PLANTS. 



231 



threads of water present in the 

 wood. The following experiment 

 leads to the same conclusion. If 

 we fix a piece of fresh fir wood in 

 the shorter limb of a U-shaped glass 

 tube, and fill the tube with water, 

 fluid escapes from the upper cut 

 surface until the pressure is com- 

 pletely equalised. A straight glass 

 tube, G (see Fig. 87), 2-4 cm. wide, 

 is closed at one end with a per- 

 forated rubber stopper, through 

 which passes the thin glass tube R. 

 Into the other end is cemented air- 

 tight a fresh piece of fir-wood (I 

 used a piece 15 cm. long and 2 cm. 

 in diameter). The tube JK, bent 

 twice at right angles, is in con- 

 nection with the flask K, which 

 in turn is connected by means of 

 the glass tube R' with an air- 

 pump. If we dip the free cut 

 surface of the wood into water 

 and exhaust, water at once filters 

 through the wood into the wide 

 glass tube. We now put together 

 the apparatus represented in Fig. 

 88. 



The very large funnel T hangs 

 in the iron ring of a heavy ring 

 stand placed on a high cupboard. 

 The tube of the funnel is connected 

 by rubber tubing with the glass 

 tube 6r, about 150 cm. in length, 

 whose lower end passes into a wide 

 glass tube, G'. The lower part of 

 this last is closed air-tight with a 

 piece of a branch of Abies pectinata 

 or Taxus baccata, A, 6 cm. long 

 and 2 cm. in diameter. The whole 



IS now 



FIG. 88, Apparatus for demonstrat- 



tilled With dlS- ing the readiness with which water 

 moves in the wocd, and the fact that 

 the closing membranes of the bordered 

 pits of the tracheides are imperforate. 



