208 



TRANSPIRATION. 



the sheet round the stem and sealing the stretched and 

 overlapped cut edges with rubber cement) is held by an 

 aluminium band in a groove below the edge of the shell. 

 Use a plant with large leaf-surface but grown in a small 



pot so as not to be too 

 heavy for the balance. 



(a) To test the influ- 

 ence of light, determine 

 and compare the loss of 

 weight, by transpiration, 

 in successive equal 

 periods in (1) direct sun- 

 light, (2) in diffuse light, 

 (3) in darkness. 



(6) To test the influ- 

 ence of atmospheric 

 humidity, set the ap- 

 paratus for equal periods 



Fig. 46.-A Pot Plant, enclosed in an Alumi- U) in moist air place 

 nium Shell, for Transpiration experiments. it below a bell- jar On a 



wet cloth, along with a 



dish of water, (2) in dry air replace the wet cloth by a 

 dry cloth, and the dish of water by a dry dish containing 

 dry calcium chloride. 



(c) Determine the influence of temperature by setting 

 the apparatus in a warm place, a cool place, and a cold 

 place. Warmth may be supplied by placing under the 

 bell- jar a dish of dry sand, and after noting the loss in 

 weight during an hour, taking out the dish of sand, heat- 

 ing the sand, and placing it again under the bell- jar. To 

 cool the air, set the apparatus in a large flower-pot, fill 

 this with sawdust up to the edge of the pot containing the 

 the plant, and above this place chopped ice, and cover with 

 a bell-jar. 



271. Influence of Water-Supply Conditions on 

 Transpiration. In the weighing experiments just 

 described, we have studied only the conditions that 

 surround the transpiring leaves, but transpiration is of 



