Jan., 1920] Resistance of Leaves to Transpiration 65 



leaves showed no rupture of living cells. The hairs were 

 removed from the half grown leaf with curved forceps, and 

 the leaves were allowed to grow to full size before the experi- 

 ments were performed. 



Series I. There are four experiments in this series, each 

 one of which has one or more of the environmental conditions 

 different from the other. The table below gives the condition 

 under which each experiment was performed. The same two 

 plants were used in each one of the experiments. 



Series I. 



Experiment 1. Darkroom, still air. 



2. Darkroom, wind. 



3. Greenhouse, still air. 



4. Greenhouse, wind. 



The purpose of changing the conditions to which the plants 

 were exposed was to see what comparative effect the conditions 

 have on the resistance of the leaves to water loss. For example, 

 wind increases transpiration, and as both plants are exposed to 

 the same wind velocity, in order to determine their com- 

 parative resistance to water loss in wind, we compared their 

 ratios in still air to their ratios in wind. If the ratios are the 

 same each plant has resisted the wind to the same degree, but 

 if they are different one of the plants has offered more or less 

 resistance to the wind than the other. By comparing ratios, 

 the resistance of the leaves to water loss under different con- 

 ditions can be determined. The ratios used in the first four 



,, transpiration of tobacco ^ , 



experiments are the-T ^- -r- t 1,-- — tor the same time 



transpiration oi mullein 



and under the same conditions, which for convenience will be 

 designated as :rr-. — . (In the tables and curves simply 



as^). 



Experiment 1. The hourly results of experiment 1, which 

 was performed in the darkroom in still air, are tabulated on 

 page 76, and expressed as curves on page 64. The tem- 

 perature, saturation, deficit, and evaporation are almost 

 constant under the conditions in the darkroom, while the 

 transpiration rates show a rhythm in the curve about the middle 



