EXPERIMENTS OF HALES. 43 



HALES, in his experiment XXXIV., cut off a vine stem 7 feet above the 

 ground, and attached to the trunk tubes of 7 feet long, joined together. Below 

 the cut there were no branches. This was done on the 30th of March, at 3 P.M. 



As the stem poured out no sap on that day, he poured water into the attached 

 tube to the height of two feet. 



This water was absorbed by the stem, so that about 8 P.M., the water had fallen 

 to 3 inches in the tube. 



The next day, | past 6 A. M., the sap stood 3 inches higher than at 8 the 

 evening before. From this time the sap continued to rise, till it reached a height 

 of 21 feet. It would perhaps, says HALES, have risen higher, had the joinings- 

 of the tubes been more water-tight. 



Whatever opinion we may entertain as to the cause of the efflux and pressure 

 of the sap, it is impossible to suppose that the mechanical or any other structure 

 or quality of the radical fibres, the spongioles, or the inner parts of the vine stem 

 generally, can have changed so much between the evening of the 30th and the 

 morning of the 31st, as to give rise to two completely opposite influences. 



On the evening of the 30th the water poured into the tube was absorbed ; on 

 the 31st it was expelled with a continually increasing force. 



In his experiment XXXVII., HALES fixed, on three branches of a horizontally 

 trained espalier vine, siphon tubes, filled to a certain point with mercury. 



The three branches received their sap from the common stem, that stem from 

 the root. The first branch was 7 feet from the second, the second 22 feet 9 

 inches from the third. The first and third branches were two years old, the 

 middle one was older. 



From the 4th to the 20th of April, the mercury stood, in consequence of the 

 pressure of the sap, higher in the open limb of the tubes than in the other which 

 was attached to the branch. 



The greatest height attained by the mercury was from 21 to 26 inches. 



On the 21st of April, when the flowering was nearly over, the sap in the middle 

 branch went backwards ; it was absorbed, and so considerably, that the mercury 

 stood 4 inches lower in the open limb than in the other. After a rainy night on 

 the 24th of April, the sap again rose in the open tube 4 inches. 



In the first (lowest) branch, the sap went back on the 29th of April, 9 days 

 after the middle one ; the third (highest) branch only began to absorb the sap on 

 the 3d of May, thirteen days after the middle one. 



We see from this experiment, as HALES observes, " That the cause which 

 produces the flow of the sap does not proceed from the root alone, but that it 

 belongs to a force inherent in the stem and branches. For the middle branch 

 followed more rapidly the changes of temperature, of dryness and of moisture, 

 than the two others, and absorbed the sap nine days before one, and thirteen days 

 before the other, both of which, during this time, poured out sap instead of 

 absorbing it. (The cause of the efflux and pressure had, in the older branch, dis- 

 appeared, and given place to an opposite influence, while it still continued active 

 in the two younger branches.) 



" The middle branch was 3 feet 8 inches higher than that next the stem. The 

 height of the mercury in the three tubes was, respectively, 14, 12, and 13 

 inches. The maximum was 21, 26, and 26 inches. These numbers prove that 

 the greater length of the middle branch had no perceptible influence on the height 

 of the mercury, as compared with that in the other tube." 



In his experiment XXXVIII., HALES observes, " Moisture and warmth made 

 the sap most vigorous. If the beginning or middle of the bleeding season, being 

 very kindly, had made the motion of the sap vigorous, that vigor would imme- 

 diately be greatly abated by cold easterly winds.* 



"If in the morning while the sap is in a rising state, there was a cold wind with 

 a mixture of sunshine and cloud ; when the sun was clouded the sap would 

 immediately visibly subside, at the rate of an inch in a minute for several inches, 

 if the sun continued so long clouded ; but as soon as the sunbeams broke out 



* Effect of cold and of shade on tte rise of the sap. 



