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bark of the root, is carried up by the alburnum, or white wood of 

 the root, the trunk, and the branches ; that it passes through what 

 he calls the central vessels into the succulent part of the annual 

 shoot, the leaf-stalk, and the leaf; and that it thence returns to the 

 bark through the returning vessels of the leaf-stalk. The principal 

 object of the present paper is to point out the causes of the descent 

 of the sap through the bark, and the consequent formation of wood. 



The causes to which he ascribes this descent are : 1 . Gravitation ; 

 2. Motion communicated by winds or other agents; and 3. Capil- 

 lary attraction, and perhaps some peculiar circumstances in the con- 

 formation of the vessels themselves, which renders them better cal- 

 culated to carry fluids in one direction than in another. 



Before he proceeds upon the experiments from which he has de- 

 duced these conclusions, he premises a few observations on the func- 

 tions of the leaf, from which all the descending fluids in the tree ap- 

 pear to be derived. He describes an experiment he made on a leaf 

 of a vine, in which its lower surface being placed in contact with a 

 clean piece of plate glass, this glass was soon found to be covered 

 with a strong dew, which had evidently exhaled from the leaf; and 

 at the end of half an hour so much water was found to have been 

 discharged from the leaf, that it ran from the glass when it was held 

 obliquely. The position of the leaf being then inverted, and its upper 

 surface being brought in contact with the glass, not the slightest 

 portion of moisture appeared, although the leaf was for some time 

 exposed to the full influence of the meridian sun. Hence it is in- 

 ferred, that the vessels intended for perspiration are confined to the 

 under surface of the leaf, and that these, like the cutaneous lym- 

 phatics of the animal ceconomy, are also capable of absorbing mois- 

 ture when the plant is in a state to require it ; whereas the upper 

 surface seems chiefly formed for absorbing light ; and if anything 

 exhale from it, it is probably vital air, or some other permanently 

 elastic fluid. 



Reverting now to the principal object of his paper, the author de- 

 scribes an experiment on a shoot of a vine, which he bent downw r ards 

 nearly in a perpendicular direction. After it had grown some time 

 in this position, and acquired a ligneous texture, he stripped the bark 

 from a part of it, and thus cut off all communication through the 

 bark between the shoot and the parent stem. Former experiments 

 have shown, that had this shoot grown in its erect position, the lip 

 of the bark above the wound would have shown an accumulation of 

 fresh wood and bark ; but in this instance the contrary was found to 

 be the case ; the lip next to the stem, w r hich by its position was now 

 uppermost, gave evident signs of this accumulation. This is ascribed 

 to the gravitation of the sap, from the curvature of the shoot down 

 to the lip. The result of this experiment seems to point out one of 

 the causes why perpendicular shoots grow with much greater vigour 

 than those which are inclined or horizontal, they having probably a 

 more perfect and rapid circulation. 



The effect of motion on the circulation of the sap was deduced 



