Transpiration and Water Movement 



99 



makes possible the entrance of the germ of the black-rot 

 disease to the cabbage and allied plants. This organism 

 is productive of one of the severest of the cabbage diseases 

 (Fig. 30). 



60. Transpiration and evap- 

 oration. Since transpiration 

 is an evaporation phenomenon, 

 it is possible to compare the 

 amount of evaporation in dif- 

 ferent habitats, and thus be able 

 better to determine or forecast 

 plant behavior in such habitats. 

 There are many difficulties in- 

 volved in employing as a meas- 

 ure the evaporation of water 

 from a freely exposed water- 

 surface. The simple evapo- 

 rimeter devised by Livingston 

 is extremely satisfactory for this 

 purpose (Fig. 31). 



This instrument affords a 

 means of measuring the evap- 

 oration from a porous cup. It 

 consists merely of a 

 bottle, or mason jar, 

 through the well- 

 paraffined stopper of 

 which passes a tube 

 connected by a rub- 

 ber stopper with some 

 type of porous cup 



FIG. 31. Simple eva perimeter, Livingston 

 form. 



