CHAPTER II. PRACTICAL EXERCISES. 235 



If, however, the growth of the grain be longer continued, the sweet taste 

 at first developed will gradually disappear, the sugar first formed from the 

 starch being now used up in the formation of new tissues. 



2. Some idea of the force with which germinating seeds imbibe water may 

 be obtained by filling a tumbler partly full of beans, pouring on water enough 

 to completely fill the interspaces, covering the beans with a sheet-iron or board 

 disc, cut to loosely fit the inside of the tumbler, and placing on this an iron or 

 lead weight. The position of the disc should now be accurately noted by 

 making a mark on the outside of the glass. After a few hours, the weight, 

 even though many times heavier than the weight of the beans, will be found to 

 be raised. 



3. Try the following experiment in osmose. Obtain a glass tube six or 

 eight inches long, having a diameter of about half an inch, and having its ends 

 cut off square. Soften one end in a Bunsen flame, and having whittled a stick 

 into conical form, run the point into the heated end of the tube and rotate it 

 so as to render the edge of the tube somewhat flaring. When this end of the 

 tube is sufficiently cool, tie securely over it an imperforate piece of bladder, 

 in such a manner as to form a sac rather large in diameter as compared with 

 the thickness of the tube. Pour into the open end of the tube a rather thick 

 solution of sugar until the liquid fills the bladder and stands an inch or so high 

 in the tube. Then immerse the apparatus in a glass vessel containing about 

 the same amount of pure water and fasten the tube in an upright position so 

 that the liquid within it will stand at about the same level as that outside. 

 After some hours, observe that the liquid within the tube has increased in 

 volume and now stands at a considerably higher level than at the beginning 

 of the experiment. Observe also that the liquid outside in the glass has a 

 sweetish taste. 



Now reverse the experiment by placing pure water in the bladder and 

 about an equal quantity of sugar solution in the glass, and observe carefully 

 the result. 



Again vary the experiment by substituting for the solution of sugar in the 

 first experiment, one of gelatin made just sufficiently dilute so that it will not 

 set on cooling. After the lapse of twenty-four hours test the water in which the 

 tube and bladder have been immersed, for gelatin, by dropping into it a solu- 

 tion made by dissolving a few grains of tannin in a little hot water. If any of 

 the gelatin has passed through the membrane and mingled with the exterior 

 liquid, a curdy white precipitate will immediately appear. Observe also 

 whether the level of the liquid in the tube has risen or fallen. 



4. Study root-pressure by means of the following experiment : Cut off the 

 stem of some thriftily growing woody plant, as for example that of the Grape- 

 vine, a few inches above the ground ; slip over the stump one end of a short 

 piece of rubber tubing and secure it firmly by means of a string ; into the other 

 fasten the open end of a glass tube bent as shown in Fig. 463 and closed at 

 the opposite end. The tube should have a little mercury in the lower bend, 

 and should be fastened in the position shown in the figure. The closed arm 

 of the tube should, for convenience, be about ten inches long. Great care 

 should be taken that the joints are perfectly tight. Note carefully the level of 



