66 PLANT PHYSIOLOGY. 



It is well to set up one of these cells for observation by the entire 

 class. Very full and clear directions are given in the pages of Goodale 

 cited above. It is rather too difficult for each student to set up sepa- 

 rately unless time is abundant. It is shown in Fig. 12. Compare also 

 Copeland, " An Artificial Endodermis Cell," Botanical Gazette, 29, 437. 

 I have had fair success in simplifying this apparatus as follows: A small 

 porous cup (obtainable at trifling cost), about 40 mm. diameter and 

 60 mm. long, is thoroughly washed. A bottle just sliding inside it has 

 its bottom removed and is then firmly sealed into the top of the cup by 

 sealing-wax. The cup is then soaked in boiled water overnight. In- 

 side of it is then placed a 3$ solution of potassium ferrocyanide, and 

 it is set in a dish of 3$ copper chloride solution, the two liquids being at 

 the same level, and left overnight. The cup is then emptied and filled 

 with molasses to which a few drops of potassium ferrocyanide are 

 added ; a rubber stopper containing a long glass tube is then inserted 

 into the neck of the bottle and the cup is plunged into water containing 

 a little copper chloride. An ascent of the inner liquid follows, and 

 no trace of the color of the molasses comes out into the outer vessel. 

 Instead of the long open tube, a short closed graduated tube may be 

 used and the pressure determined by the compression of the air above 

 it by Boyle's law (see page 68). In preparing this the tube should be 

 drawn to an open capillary point, and sealed when the liquid has reached 

 the zero mark of the scale. The bougies of Pasteur filters make excel- 

 lent cups, but are more expensive. In using all such cups it is neces- 

 sary that the rubber stopper should not come into contact w r ith the cup 

 itself, since its yielding under pressure would leave the membrane dis- 

 continuous. Where it must touch the cup, the latter should have a layer 

 of sealing-wax extending below the stopper. It is not difficult to seal the 

 tube into the bottle or bougie with sealing-wax. (See Note i of the Ad- 

 nenda). 



24. Do roots actually absorb water in quantity and pass it up 

 stems ? 



Answer by observation of Experiment 9. 



EXPERIMENT 9. This may be tested by cutting off all but the root 

 and lower part of the stem from a vigorous plant and noting whether 

 water is forced out of the cut surface by the roots. Select a vig- 

 orous single-stemmed herbaceous plant, and cut it off an inch from 

 the ground. To the stump attach a burette by a water-tight joint 

 (see page 40) ; fill the burette to 2 cm. above the zero mark with 

 water (to allow measurement in case it drops), add a film of oil to 

 prevent loss by evaporation, and note the rise or fall of the liquid. 

 (See Fig. 10.) A Ricinus is very good for this experiment. 



Compare this arrangement with that of Experiment 6. 



