344 Curtis : The Work Performed in 



during the experiment was sufficient to cause a much quicker ac- 

 celeration of rate than in the preceding example. 



In the third experiment a length of stem immersed in water at 

 23 ° was tested under pressure. The rate of 55.8 was lowered, 

 when the stem was covered with water at 8°, within five minutes 

 to i 20 , and dropped rapidly to I 34 . Water at 25 ° was now introduced 

 and the first measurement a few minutes later showed a rate of I 25 

 followed by a sharp rise. The temperatures given are probably 

 near those of the stem since the thermometer was lying in the dish 

 against the stem and they would not vary materially in taking on 

 the temperature of the surrounding media. The final test illus- 

 trates the variations of rate at different temperatures. The read- 

 ings are not consecutive. The results are rather suggestive as in- 

 dicating the very considerable additional work placed upon the 

 plant by variations of temperature. These changes are often sud- 

 den and not only act upon the transpiring organs but also intro- 

 duce a very considerable resistance that is frequently overlooked. 



Resistance Introduced by Cuttings 



The localization of resistances noted above led, for the pur- 

 pose of comparison, to measurements on the effect of the intro- 

 duction of resistances by cutting. The tests were confined to 

 Tar us as these plants will better stand the treatment without flag- 

 ging. In the first column is given the transpiration rate of the 

 branch and in the second and third columns the rates when the 



stem was cut y 2 and ^ through. The fourth column shows the 



rate when the column was reduced to a few sq. mm., indicated at 

 the right of the column. 



VI. 



sq. mm. S q. m m. 



Taxus 89 14 13 6 9.5 24 12 19 29 8 8X1-5 



81 9-5 13-5 12.8 10 14 20 34 



8 8.9 13.2 12.2 9 16 20 34 



8.4 8.4 13 13 9 l6 20 37 



8 8.9 13.6 13 10 15 21 , 36 



8 - 2 9 12 13 10.5 14 22 37 



Taxus 28.5 29.5 30.8 35 2 29 15 44 90 184 7 7X -9 



28 29 30.4 36 30 45 98 196 



29.2 29 30 35 29.5 48 102 186 



28.5 28.5 30.1 39 29.5 4 6 96 200 



28.4 29 29.5 36 30 47 98 189 



28.5 28.5 30 36 29 46 98 198 



