238 



EXPERIMENTS WITB PLANTS 



Oak would seem to have an advantage in this respect 

 over the Pine. In order to compare their efficiency, 

 cut a live branch of each about twelve inches long and 

 as free from leaves or branches as possible. 

 Eemove the leaves and branches which 

 are present, and connect the base of the 

 branch by means of two or three feet of 

 heavy white rubber tubing to a glass tube 

 three or four feet long (the tube may be 

 formed of several pieces joined together 

 by rubber tubing) . Hold the tube upright 

 with the branch hanging straight down, 

 and fill it with water; compress the rubber 

 tube several times to expel air. Place the 

 branch upright and secure it by a clothes- 

 pin in the position shown in Fig. 140 

 (which shows a slightly different arrange- 

 ment from the one here described). Con- 

 nect the upper end with a piece of glass 

 tubing (about six inches long) , in which 

 place a little water. Place a little oil on the 

 top of the water in each of the tubes. Make 

 the joints water-tight by winding with elas- 

 tic bands (or with wire) ; close with sealing-wax 

 any wounds made by the removal of leaves, branches, 

 etc. The diameters and lengths of the branches should 

 be as nearly alike as possible. The height of the 

 water-column in the long tubes (measured from the 



140. Arrange- 

 ment for f orc- 

 ing water 

 t h rough a 

 branch. 



