132 ON THE INVERTED ACTION 



I shall now proceed to relate, to be also capable of an inverted action, 

 when that becomes necessary to preserve the existence of the plant. 



As soon as the leaves of the oak were nearly full grown in the last 

 spring, I selected in several instances, two poles of the same age, and 

 springing from the same roots in a coppice, which had been felled about 

 six years preceding ; and making two circular incisions at the distance 

 of three inches from each other, through the bark of one of thejpoles on 

 each stool, I destroyed the bark between the incisions, and thus cut off 

 the communication between the leaves, and the lower parts of the stem 

 and roots, through the bark. Much growth, as usual, took place above 

 the space from which the bark had been taken off, and very little below it. 



Examining the state of the experiment in the succeeding winter, I 

 found it had not succeeded according to my hopes ; for a portion of the 

 alburnum, in almost every instance was lifeless, and almost dry, to a 

 considerable distance below the space from which the bark had been 

 removed. In one instance the whole of it was, however, perfectly alive ; 

 and in this I found the specific gravity of the wood above' the decorti- 

 cated space to be 1.114, and below it, 1.111 ; and the wood of the un- 

 mutilated pole, at the same distance from the ground, to be 1.112, each 

 being weighed as soon as it was detached from the root. 



Had the true sap in this instance wholly stagnated above the decor- 

 ticated space, the specific gravity of the wood there ought to have been, 

 according to the result of former experiments*, comparatively much 

 greater ; but I do not wish to draw any conclusion from a single experi- 

 ment ; and indeed, I see very considerable difficulty in obtaining any 

 very satisfactory, or decisive facts from any experiments on plants, in 

 this case, in which the same roots and stems collect and convey the sap 

 during the spring and summer ; and retain within themselves that which 

 is, during the autumn and winter, reserved to form new organs of assimi- 

 lation in the succeeding spring. In the tuberous-rooted plants, the roots 

 and stems which collect and convey the sap in one season, and those in 

 which it is deposited and reserved for the succeeding season, are per- 

 fectly distinct organs ; and from one of these, the potato, I obtained 

 more interesting and decisive results. 



My principal object was to prove, that a fluid descends from the leaves 

 and stem, to form the tuberous roots of this plant ; and that this fluid 

 will in part escape down the alburnous substance of the stem, when the 

 continuity of the cortical vessel is interrupted. But I had also another 

 object in view. 



* See above, No. V. 



