252 SMITH : 



Thus the first day shows on the average the leaves with the 

 stomata inwards "9° C. hotter than those with stomata out- 

 wards. The sec6nd day shows 2 "9° C. difference, and the 

 third day 2 * 6° C. I am not able to account for the smaller 

 difference on the first day. The only marked difference from 

 the second and third days is in the humidity, which was much 

 lower, but it is not obvious that this should tend to equalize 

 the temperatures. If we take the average of the whole twenty 

 readings on the three days, we get stomata outwards 10 • 7° C. , 

 stomata inwards 12*9° C, a difference of 2 '2° C. , and this is 

 very near to the 2*1° C. obtained by readings with the single 

 apparatus. 



We may take it that in direct sunlight of this intensity and 

 for still air the loss of water by transpiration cools the leaf 

 from 2°-3° C. at least. Most probably greater differences 

 would be obtained if the edges of the leaves were accurately 

 fitted together all round so that no water vapour could escape. 

 One of the leaves with stomata inwards, which reached a 

 temperature of 45° C. , was turned brown on each side of the 

 lower portion of the midrib for a distance of 1-2 cms. Drops 

 of water stood plentifully on the inside of these leaves when 

 they were taken apart. The same experiments were also 

 performed on two pairs of the young red flaccid leaves of 

 Amherstia nohilis, and gave the same general results. These 

 are set out in Table XXII. 



Table XXII.— December 27, 1906. 



Two pairs of young red flaccid leaves of Amherstia nohilis : 

 one pair with stomata outwards, the other with stomata 

 inwards. 



Time : 1 1 . 53 a.m. 



Black bulb : 62 • 2. 



Shade temperature : 26 • 4. 



Humidity : 69 per cent. 



Leaf temperatvire : 39-2, 36-9. 38-8, 37-2. 39-6, 38-6, 41-3, 43'7, 

 41-9, 40-6, 43-7, 40-6. 



Conditions : Bright sun. No breeze when highest temperatures 

 are recorded ; slight breeze for lower. 



