237 



appears to militate against the above hypothesis, namely, that when 

 two circular incisions are made, at a small distance from each other, 

 through the bark, round the stem of a tree, and the bark between 

 these incisions is wholly taken away ; that portion of the stem which 

 is below the incisions continues to live, and to increase in size, though 

 much more slowly than the parts above the incisions. The above- 

 mentioned naturalists have also observed, that a small elevated ridge 

 is formed round the lower lip of the wound, which makes some slight 

 advances to meet the bark and wood, projected in larger quantities 

 from the upper lip of the wound. 



Our author, in a former paper, attempted to explain the above cir- 

 cumstance, by supposing that a small part of the true sap, descending 

 from the leaves, escapes downwards, through the porous substance 

 of the alburnum : in another paper he has shown, from the growth 

 of inverted cuttings, the existence of a power in the alburnum to 

 carry the sap in different directions ; and he now describes some ex- 

 periments made in order to show that the conclusions drawn by him 

 are not inconsistent with the facts stated by Hales and Du Hamel ; 

 and that although the ascending sap usually rises through the al- 

 burnum and central vessels, yet the alburnous vessels appear to be 

 also capable of an inverted action, when such action becomes neces- 

 sary to preserve the existence of the plant. 



The first experiment described in the present paper, consisted in 

 removing the bark by means of circular incisions at the distance of 

 three inches from each other from the stems of several young oaks, as 

 soon as the leaves were nearly full grown, and examining, in the 

 succeeding winter, the state of the parts. In almost every instance 

 the alburnum was found to be lifeless, and almost dry ; in one in- 

 stance, however, it was perfectly alive ; and in this the specific gra- 

 vity of the wood, above the decorticated space, was 1114, and below 

 it 1111, whereas the specific gravity of an unmutilated stem, from 

 the same roots, and at the same distance from the ground, was 1112. 

 Now if the whole of the descending, or true sap, had in the above 

 instance stagnated above the decorticated part, the specific gravity of 

 the wood there ought to have been much greater than it was found 

 to be. 



Mr. Knight, conceiving that he should obtain more satisfactory 

 and decisive results from tuberous-rooted plants, now proceeded to 

 make some experiments on the potatoe. The early varieties of this 

 plant, as is well known, afford neither blossoms nor seeds. This cir- 

 cumstance he attributed to the privation of nutriment, from the pre- 

 ternaturally early formation of the tubers ; he therefore planted, in 

 the last spring, some cuttings of a very early variety of the potatoe 

 in garden-pots ; and when the plants had grown a few inches high, 

 they were secured to sticks, fixed erect in the pots. The mould was 

 then washed away from the base of the stems, so that the plants were 

 suspended in the air, and had no communication with the remaining 

 soil, except by their fibrous roots. Efforts were soon made, by every 

 ~!ant, to produce runners and tuberous roots, but these were de- 



