MOTION OF THE SAP OF PLANTS. 79 



face of the twigs and leaves, the water fell (Xlth 

 experiment), in one hour, 36 inches. He now cut 

 off the branch 13 inches below the tube, and placed 

 the portion cut off (with the twigs and leaves) ver- 

 tically in a vessel of water. This last absorbed, in 

 30 hours, 18 ounces of water, while the portion of 

 wood remaining in connection with the tube, which 

 was 13 inches long, only allowed 6 ounces of water 

 to pass, and that under the pressure of a column of 

 7 feet of water. 



HALES shews, in three other experiments, that the The motion 



of the sap is 



capillary vessels of a plant, alone, and in connection caused by 

 with the uninjured roots, are easily filled with water rating sur- 

 by capillary attraction, without, however, possessing 

 the power of causing the sap to flow out and to rise 

 in a tube attached. The motion of the sap, con- 

 cludes HALES, belongs to the evaporating surface 

 alone ; he proves that it goes on in an unequal 

 degree from the stem, the twigs, the flowers and 

 fruit, and that the effect of the evaporation stands 

 in a fixed ratio to the temperature and hygrome- 

 tric state of the air. If the air were moist, but 

 little was absorbed ; the absorption was hardly per- 

 ceptible on rainy days. 



He opens the second chapter of his Statistics 

 with the following introduction : 



" Having in the first chapter seen many proofs of 

 the great quantities of liquor imbibed and perspired 

 by vegetables, I 'propose in this, to inquire with 

 what force they do imbibe moisture. Though vege- 



