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upon a sloe-stock, the graft will grow rapidly, but not so the stock, 

 which retains its slow-growing character ; a striking example of the 

 permanency of the specific life of the stock, and, as it appears to me, 

 affording a fatal argument against the pretended descent of the sap. 

 If a descending bark- sap existed, the sloe-stock would be naturally 

 covered with annual rings of plum wood from the graft, and it would 

 grow in proportion to the growth of the graft, but this is by no 

 means the case, for the new annual rings are formed, not out of a 

 descending bark-sap, but out of a cell development of the cambium 

 already existing in the stock, and having essentially the same charac- 

 ters. The formation of new wood of the nature of the graft has 

 always been taken for granted, in order to prove the descent of the 

 bark-sap ; but we find that this wood does not partake of the nature 

 of the graft, and that it must, therefore, be formed independently of 

 any descending juices." These being the views held by the best 

 authorities on the matter at present, I shall now detail my experi- 

 ments, and show how far they bear on either. 



My predecessor, Mr. Niven, had been conducting some physiologi- 

 cal experiments before he left the Botanic Gardens, the results of 

 which are already before the public. I consider it, however, only 

 just on my part towards him, that I shall here state my principal 

 experiment to be founded on one he had commenced, though we do 

 not appear to have been aiming to attain similar objects. He had 

 cut several trees more or less through their boles in various ways, one 

 of them a large horse-chestnut tree, then four feet in circumference, 

 and now four feet nine inches. At three feet from the surface of the 

 ground, two deep incisions had been made through the stem, crossing 

 each other at right angles, and reaching the circumference on each 

 side. The tree was thus left growing on four separate pillars of wood, 

 alburnum and bark, but no results, that I am aware of, were deducible 

 from this experiment when I commenced the following. Seeing that 

 it afforded an excellent example for observing the growth of woody 

 matter, as it would form to fill up the y^erforations through the stem, 

 I examined the portion of the tree where it was cut, and found that 

 the heart-wood was completely dead, and beginning to decay, at both 

 the upper and lower lips of the cut. It therefore could render no 

 assistance whatever for the phenomena of life being carried on through 

 its medium. The ascent of the sap and formation of wood must, then, 

 have depended altogether on the functions of the alburnum and cam- 

 bium, which rested on the four pillars of dead wood, now simply 

 acting as supports. During the spring of 1839, I had one of the pil- 

 lars laid bare, thus confining the life-supporting action to the remain- 



