358 APPENDIX C. 



the ao^e of Newton. They deserve a place in every work treat- 

 ing of the physiology of plants. 



In the beginning of his work Hales describes the experiments 

 made by him on the motion of the sap in vegetables arising 

 from the exhalation from their surface. These experiments 

 were made with leafy branches, plants cut off from the roots, 

 and others still retaining their roots. 



The force of the pressure of a column of water, both with 

 and without the cooperation of exhalation, was shown by the 

 following experiment. 



He fixed an apple-branch, three feet long, half-inch in diameter, 

 full of leaves and lateral shoots, to a tube seven feet long, and 

 five-eighths of an inch in diameter. He filled the tube with 

 water, and then immersed the whole branch up to the lower end 

 of the tube, in a vessel fall of water. The water was driven 

 into the branch by the pressure of the column of water in the 

 tube, which subsided fourteen and a quarter inches in two 

 days. 



On the third day he removed the branch and tube out of the 

 water, and hung it up in the open air ; the water in the tube fell 

 now twenty-seven inches in twelve hours. 



To determine the comparative force with which the water is 

 driven through the vessels of the ligneous body by pressure alone, 

 and by pressure and exhalation combined. Hales joined a leafy 

 apple branch to a tube nine feet long filled with water. In 

 consequence of the pressure of the column of water and of the 

 exhalation taking place from the surface of the leaves and 

 twigs, the water in the tube (fortieth experiment) sank 36 inches 

 in an hour. He then cut off the branch 13 inches below the 

 glass tube, and placed the cut portion (with leaves and twigs) 

 upright in a vessel with water. It was found to imbibe 18 ozs. 

 of water in 30 hours ; in which time only 6 ozs. of water had 

 passed through the 13 inches of the stem connected with the 

 tube, and that too under the pressure of a column of water 

 7 feet high. 



In three other experiments, Hales shows that though the 

 sap-vessels of plants will imbibe water plentifully by capillary 

 attraction in branches severed from the trunk, as well as in 

 those left in connection with the uninjured roots, they have 



