80 



WATER AND MINERAL NUTRIENTS 



during the summer. For every ounce of dry matter pro- 

 duced, it is estimated that fifteen to twenty-five pounds 

 of water must pass through the plant. Cut off a succulent 

 shoot of any plant, press the end of it through a hole in a cork 



and stand it in 

 a small bottle of 

 water. Invert 

 over this bottle 

 a large-mouthed 

 bottle (as a fruit- 

 jar), and notice 

 that a mist soon 

 accumulates on 

 the inside of the 

 glass. In time, 

 drops of water 

 form. The ex- 

 periment may be 

 varied as shown 

 in Fig. 128. Or 

 invert the fruit- 

 jar over an entire 

 plant, as shown 



128. To illustrate transpiration. • p- inq tak- 



ing care to cover the earth with oiled paper or rubber cloth 

 to prevent evaporation. 



167. Even in winter, moisture is given off by leafless 

 twigs. Cut a twig, seal the severed end with wax, and allow 

 the twig to lie several days : it shrivels.. There must be some 

 upward movement of water even in winter, else plants would 

 shrivel and die. 



168. When the roots fail to supply to the plant sufficient 

 water to equalize that transpired by the leaves, the plant 

 wilts. Transpiration from the leaves and delicate shoots is 

 increased by all of the conditions that increase evaporation, 



