071 Vegetable Physiology. 169 



the same part of the tree; that is, through the camhium or 

 jpulp^ hetvoeen the hark and alhurnum. I thought, by. the ap- 

 plication of some medium of moisture, I might be able to prove 

 the supposition. This was done by an application of moss to 

 both edges of the one side of the ring. In about fourteen days 

 after this application, I found that the supposition had been 

 correct. The specimens before you exhibit a repetition of the 

 same result, in both stages ; presenting, in my humble opinion, a 

 very important fact; namely, that there appears, exterior to the 

 wood itself, two perfectly distinct principles : the one passing up- 

 wards from the roots, to the developement of leaves, which 

 I would call ihe leaf principle, for 1 find it cannot be changed ; 

 and the other passing downwards from the leaves, to the develope- 

 ment of roots, which I would call the root principle, and which 

 also appears to be equally permanent. I am consequently dis- 

 posed to maintain, that from any part of the surface of the woody 

 structure these two develop e'ments are to be found ; and it appears 

 to me only a modified example of the descending one, when we 

 see roots proceeding from the stems of such genera as the i^icus, 

 Pothos, and many others. 



A very satisfactory proof of this is found in the case of pro- 

 pagating plants from cuttings. Each cutting appears to contain 

 within itself so much of the two -principles, that it only requires 

 to be placed under such circumstances of atmosphere as will 

 tend to preserve the action of the leaves without collapsing, 

 until the descending principle has had time to ramify itself through 

 their action, into roots ; when, by a gradual removal of the bell- 

 glass, the plant is prepared to perform its various functions 

 unaided, as well as to meet the viscissitudes of a constantly 

 changing atmosphere. The one principle, I have no doubt, will 

 be found to proceed principally from the soil, to the expansion of 

 leaves ; and the other from the combined agency of the atmosphere, 

 to ihe forfnation of new wood and roots, and the extension of the 

 roots. Corresponding with these views, some eminent phytoloo-ists 

 hold the opinion, that "when a bud shows itself at the base of a 

 leaf, or on a branch or stem, it follows two opposite movements; one 

 upwards towards the air, the other downwards towards the earth. 

 By the upward movement a new branch is produced ; whilst the 

 downward movement gives origin to a great number of new fibres, 

 which lengthen out between the bark and the wood of the 

 mother branch, as well as of the trunk down to the extremities 

 of the roots." This opinion, another learned gentleman saj's, 

 " rests entirely upon vague conjecture and hypothetical reason- 

 ing; and it appears to him the most fancif id ax\6. baseless opinion 

 ever propounded." The opinions of such authorities being so 

 much at variance on these matters, I am sure the learned gentle- 

 man alluded to will unite with me in thinking that it is de- 



