WORK OF THE SHOOT 93 



accounted for by differences in the distribution of 

 stomata ? 



Take two evergreen leaves, as nearly alike as you can 

 find, and coat the upper surface of one leaf and the under 

 surface of the other with vaseline. Carefully weigh each ; 

 then expose both to air for half an hour or more, and weigh 

 again. What difference do you find ? How does this 

 result compare with your previous experiments ? As 

 previously seen, a cut shoot placed in water absorbs a con- 

 siderable amount of liquid, and we now see that water, 

 in the form of vapour, is given off from the leaves through 

 the stomata. 



Let us now try to determine the rate at which this 

 water travels, and the amount absorbed in a given time. 

 To do this, arrange an experiment as shown in Fig. 56. 

 Take a wide-mouthed bottle provided with a tight-fitting 

 rubber stopper with three holes. Through one is passed 

 the tube of a funnel provided with a tap. Through the 

 second is passed a bent, thick-walled capillary tube, 

 passing only to the lower level of the stopper. Behind 

 the tube is a scale marked in inches or centimetres. Through 

 the third hole is passed a shoot which has previously 

 stood in water (Rhododendron or Laurel will answer very 

 well). Fill the bottle completely with water and press 

 the stopper, together with shoot and tubes, firmly into the 

 bottle. If the tap of the funnel is open, water rises in the 

 tubes. Now close the tap and fill up the reservoir. By 

 opening the tap, water flows along the bent tube and drops 

 from the open end. Now close it, and the water stops 

 immediately. As the shoot absorbs, water is drawn back 

 along the tube and readings may now be made. Care 

 should be taken that the temperature is fairly constant. 

 Obtain the capacity of the tube and determine the amount 

 of water absorbed in a given time. 



By turning the tap, the tube may be refilled and the 



