INTERNAL TEMPERATURE OF LEAVES. 



271 



whole apparatus, except the galvanometer, was now duplicated, 

 so that readings of the two kinds of leaves could be taken 

 consecutively, only the very short interval necessary to change 

 the wires of the galvanometer from one apparatus to the other 

 intervening between the readings. Though a breeze sometimes 

 sprang up or the sun was obscured during the changing of 

 the wires, yet, as a rule, the leaves were measured under the 

 same conditions by this method. The two apparatuses were 

 carefully compared and calibrated previous to observations. 



The following results were obtained : — 



Table XXXV.— December 8, 1906. 



Time. 



A.M. 



Black TT • li Air Matixre Leaf Young Leaf. 



Bulb. ^* Movement, above Air. above Air. 



Per Cent. 



8-2 

 6-3 

 8-4 

 9-0 



9' 

 13- 



12-8 

 10-0 



10' 

 12' 



lO-l 



The result here is in agreement with that of the last table 

 in showing a slightly higher temperature in the mature leaf. 

 The flaccid leaf has a midrib, which projects considerably on 

 the under side. The junction was now placed further back 

 in this midrib, so as to be further away from the lamina of the 

 leaf. The results are now not strictly comparable with those 

 for the mature leaf in which the j miction is in its original 

 position. The following readings show that the junction in 

 this position is considerably cooler, and thus illustrate the 

 delicacy of the manipulations and the care necessary to obtain 

 exactly equal conditions : — 



Table XXXVI.— December 8, 1906. 



Time. 



A.M. 



11. 



Black Himaidity. Air 



Bulb. Per Cent. Movement. 



60-0 .. 66 .. Still 



Mature 

 Leaf. 



11-2 

 11-5 

 12-2 



Young 

 Leaf. 



7-5 

 7-9 

 7-5 



