ACTION OF LEAVES. 47 



earth in the pot could be watered. After fifteen days, 

 viz., from July 3 to August 8, he found, upon making 

 all necessary allowances for waste, that this sunflower 

 plant 3i feet high, with a surface of 5616 square 

 inches above the ground, had perspired as follows: — 



Ounces 

 Avoirdupois. 



In twelve hours of a very dry warm day . 30, 



On another day 20, 



In a dry warm night without dew ... 3, 

 In a night with some small dew . . . ; 

 and that when the dew was copious, or there was 

 rain during the night, the plant and pot were 

 increased in weight two or three ounces. Other per- 

 sons have instituted other experiments of a similar 

 nature, the result of all which is, that the insensible 

 perspiration of plants is very considerable.* Hales 



* The amount of this force is strikingly illustrated by the fol- 

 lowing circumstances recorded by the late Mr. Braddick. " One 

 experiment I will mention, as it may serve to show the great power 

 of the rising sap in the vine, while its buds are breaking. On the 

 20th of March, in the middle of a warm day, I selected a strong 

 seedling vine five years old, which grew in a well prepared soil, 

 against a south-west wall ; I took off its head horizontally with 

 a clean cut, and immediately observed the sap rising rapidly 

 through all the pores of the wood, from the centre to the bark. I 

 wiped away the exuded moisture, and covered the wound with a 

 piece of bladder, which I securely fastened with cement, and a 

 strong binding of waxed twine. The bladder, although first drawn 

 very close to the top of the shoot, soon began to stretch, and to rise 

 like a ball over the wound ; thus distended, and filled with the sap 

 of the vine, it felt as hard as a cricket ball ; and seemed to all 

 appearance, as if it would burst I caused cold water from a well 



