ON VEGETABLE ORGANOGRAPHY AND PHYSIOLOGY. 225 
tion, whether upward, downward, or laterally. That the bark 
possesses in itself an appropriating elaborating principle,” is wholly 
unknown to us ; and the proof adduced in support of the allegation is 
not at all conclusive, because the union of the transferred piece with 
that to which it is removed, depends entirely on the manner in which 
it is raised from the parent stem. If all the layers of bark, with the 
vital membrane or indusium attached, be removed to a cavity made in 
another tree to receive it, a union will take place, and the subsequent 
effects will be as you have stated; but if the living membrane be not 
removed with the first, nor cut into in forming the new place, no union 
can possibly take place ; because every layer of bark, from the moment 
it is perfectly formed, and takes the name of liber, ceases to be imbued 
with life ; and though it, for a year or two, be employed in the conduc¬ 
tion of the fluids, it retains no vital energy to unite with any other 
body. Neither the last-formed layer of inner bark, nor the last- 
formed layer of wood, retain a particle of vitality after they are once 
formed. 
You ask—“ Do you not consider the sap necessary to the vigorous 
development of your indusium ? ” Most assuredly we do; but we are 
equally sure they are not identical, although, in the absence of either the 
one or the other, no increase or expansion can take place. The first 
may be called the soul, and the other the growing part of the body of 
the plant. You seem to conclude, that if a man knows how to graft, 
or bud, or propagate plants by the usual means, it signifies nothing to 
him to know which member of the plant it is that forms the union, or 
ejects the new roots. We admit that a man may be an excellent gar¬ 
dener without knowing a tittle of vegetable physiology; but how would 
he be laughed at if he were heard to declare that the union of the graft 
and stock takes place by the inosculation or adhesion of the two libers 
or the two alburnums; or that all new roots were produced by or from 
those members! You say you have doubts of the existence of the 
indusium, because you have never seen it. What! never seen the 
cambium of those writers whence you have apparently borrowed the 
tenets of your physiological creed? Why, it is as visible all the 
summer as is any other member of the stem; and, during that season, 
you may identify it with the liber then forming, if you please, but not 
with that of the former year. 
You appear to have no doubt but that a purely homogeneous and 
elaborated sap may be changed into wood and bark, though you cannot 
admit that an already organised member, scarcely visible in the winter, 
can be expanded into perfect form and consistence before the following 
VOL. v.-— NO. LX. 
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