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

 of the cambium already existing in the stock, and having es- 

 sentially the same characters. 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 anv de- 

 scending juices.' These being the views held by the best 

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

 experiments, and show how far they bear on either. 



" My predecessor, Mr. Niven, had been conducting some 

 physiological experiments before he left the Botanic Gardens, 

 the results of which are already before the Public. I consider, 

 however, it 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-chesnut tree, then four feet in circum- 

 ference, 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 (Fig. 1). 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 perforations 

 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 



