REMARKS ON VEGETABLE PHYSIOLOGY. 



the least degree necessary to assume the motion of any descending proper juice or bark 

 sap which certainly does not exist." 



" When an apricot graft grows from the trunk of a plum tree, the latter is naturally and 

 by degrees clothed with apricot wood, for out of the same soil, an apricot tree would 

 merely take up the same sap as the plum tree; but afterwards, in proportion as the leaves 

 and branches of the plum tree, or of the apricot, evaporate, assimilate, &c., plum or apri- 

 cot wood will remain." Such is Dr. Schleiden's mode of reasoning, and really the case 

 of the graft presents at first sight the strongest olyection to the descending sap theory, be- 

 cause if the new woody matter is prepared in the leaves and is deposited by a downward 

 process, is it not reasonable to suppose that when the pear grows on a quince stock, new 

 layers of pear wood will be deposited on the quince.'' But no such phenomenon occurs, 

 and as I believe for this reason. The cambium or elaborated sap, is only a prepared condi- 

 tion of the food of trees, and when it happens, as in the case of the pear on the quince, 

 that one species prepares cambium for itself and another, each one receives it as food only 

 and appropriates it to its own peculiar formation in the way that two species of plants will 

 grow in precisely the same soil without losing their identity, or two species of animals 

 subsist on the same food without assuming any degree of similarity. I do not doubt, nor 

 is it denied, that I am aware of, by any physiologists that the sap undergoes a certain de- 

 gree of elaboration in the cells and organs of the stem, but that it \s principally performed 

 by the leaves, and that the principal part of the new wood is formed by the descending 

 prepared sap, seems most in harmony with the facts that daily occur to us in practice. 



P. B. 



Rochester, N. Y., April, 1S51. 



Remarks. — A highly interesting communication. Dr. Scrleiden, in someof his works, 

 reasons so poorly that we have little ftiith in him. Experiments, which may be repeated 

 by any one, prove the passage of the fluids downward, after having risen to the leaves, and 

 been exposed to a distinct process there. The assimilation or digestion is however not 

 completed in the leaf, but depends for that final individuality of character which causes 

 it to make plum or pear tree wood, upon the bark which immediately overlays such Avood 

 — for the downward current usually passes through the bark, and is thence distributed 

 horizontally through the medullary raj's into the interior of the stem. Hence, whatever 

 the bark is which covers any part of the stem of a tree, such will be the kind of wood de- 

 posited beneath that bark — no matter w"hether the leaves above that bark be pear or quince. 



This is not only proved by the familiar fact, that the barks above and below the graft, 

 always maintain their original line of distinction, but more clearly by the experiment 

 made by phiysiologists of grafting rings of the bark of various allied species, as the pear, 

 quince and apple, upon different parts of the same trunk. After growing several years it 

 was found that the pear bark had deposited pear wood — the quince bark, quince wood, 

 and so of the others. There were no leaves to each ring of bark, and the experiment 

 clearly proved that the action of the wood depends on the bark which overlays it, and 

 gives its final character to the downward currant of fluid nutriment just as it undergoes 

 its last change into solid matter. Ed. 



