1035 



the last experiment ; but the part below the ligature had undergone 

 no change whatever : not the slightest addition had been made either 

 to the wood or to the bark. 



" 32. The sucker which was left, the only remaining one, still con- 

 tinued to grow, increasing in size above the ligature, but not in the 

 least below it. Its leaves were as large, and with the exception of a 

 slight yellowish tint, appeared as healthy, and remained as long at- 

 tached to the plant as those of the suckers which sprang from the 

 same root, but had not been experimented upon. 



"33. In the spring of the next year (1847), at the period when all 

 the leaf-buds of the unconstricted suckers began to swell and develope 

 themselves, those of the constricted one rapidly withered. Up to this 

 time they were as large, and appeared as healthy, as those of the other 

 suckers. 



"At the commencement of June (1847) this sucker was cut and ex- 

 amined. The part of the stem above the ligature had received a layer 

 of wood, and an addition of bark to that of the preceding year. The 

 part included in the ligature it was not considered necessary to ex- 

 amine. The part below the ligature had received no addition whatever 

 to the wood of the last year, and the whole thickness of the stem had 

 lost its natural aspect, appearing brown and destitute of vitality, 

 whilst the part above the ligature was of a greenish colour, and had a 

 healthy appearance." — p, 15. 



From these experiments the author concludes, as the ligature al- 

 lows the ascent of the crude sap without permitting the elaborated 

 sap to pass below it, — the formation of wood and bark going on 

 above after it has ceased below the ligature — that the ascending and 

 descending fluids pass by different channels, and that the elaborated 

 sap does not descend along the intercellular tissue ; and farther, that 

 w^hen the new wood does not extend below the ligature and does not 

 communicate with the root, vegetation ceases in the entire shoot, first 

 below, then above the ligature ; proving the layers of wood to be in- 

 dependent of each other, and also proving the necessity for each 

 layer's having a separate connexion with the roots. Seeing the de- 

 scending sap does not pass along the intercellular tissue, and seeing, 

 moreover, that the cells do not communicate with each other, the 

 descent of elaborated sap must take place through the vessels, 

 which are continuous passages extending from the leaves to the roots, 

 and having large and well-defined openings of communication with 

 each other, the anatomical requirements of tubes for the transmission 

 of fluids. The paragraphs which follow those whence the foregoing 



