GARDENING AS A SCIENCE. 
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that of the scion slipping downward into the tongue of the stock. The theory 
of this operation presumes that the juices of the latter are somewhat more active 
than those of the scion, the buds, however, of which are somewhat swollen, and 
prepared to expand under the impulse of the ascending sap. As a vital union of 
parts can only be produced by the agency of the fluid cambium, which connects 
the bark (liber) and sap-wood (alburnum) bark must be applied against bark, on 
one edge of the slips at least, and in all the four edges of the corresponding tongues. 
Tying, by means of ligatures, claying, and a super-covering of wet moss, are 
auxiliaries used to retain moisture, and exclude the oxidizing influence of the 
surrounding air. 
Under favourable conditions of a mild, and rather cloudy April, with gentle 
showers, a union may be effected, and growth proceed in a few weeks ; under 
other circumstances, a scion may live, yet remain quiescent till after midsummer. 
Be this as it may, not only does the cambium of scion and stock intercommunicate, 
and the laborated fluids of the new leaves pass downward from the scion to the 
stock, but a lateral, or horizontal flow takes place through the cellular substance of 
the medullary processes, from the bark of the scion to, and into, the alburnum of 
the stock. These processes, which also have been called divergent rays, were con- 
sidered by Mr. Knight to originate in the liber, and to converge toward the 
medulla, and not diverge from it. He was perhaps quite correct, and so, in prin- 
ciple, may be Mr. Main ; who identifies his indusium, or vital membrane, with 
the organized matter which we style cambium. 
But the grand phenomena of grafting remain still to be considered : and to lead 
to the subject, we ask, (in the character of the inquiring reader,) why are all the 
future developments of the tree, above, that is, out of the graft, exactly similar to 
it, not partaking of, or evincing any disposition to conform to those of the crab- 
stock ; and why, if any shoot protrude from the latter, although it be within half 
an inch of the point of junction, it is true to the crab, that is to itself? 
When the tree was first grafted, the crab-stock, we have supposed, was three 
quarters of an inch broad, the scion being estimated at half that size. In a few 
years, the latter shall have produced a large and fruitful head, furnished with 
more than a hundred shoots ; the former is thickened so that it measures a foot in 
the girth. Yet no shoot has been permitted to grow from it, and all its descending 
sap must therefore have been derived from the head of the tree. 
It will therefore be evident, that as the matter of woody fibre, with inter- 
spersed cellular tissue, and a horizontal convergent system, are the substances 
which cause the enlargement of the trunk, those substances are accessories only, 
but totally deficient of any of those germs or vitalized buds which produce new 
growing shoots : and hence it follows that the scion, with its two or three buds, 
comprise all the microcosm, the molecular progeny of every future member of 
growth and fertility. On the other hand, the stock contains an infinite number 
of germs, or systems of life, capable of development when called into actionby certain 
processes of stimulation. 
