IMPROVEMENT OF PLANTATIONS. 597 
in the winter." Now, this effect couUl only have been produced by 
the intermixture of some matter that had previously been prepared 
by organized vessels above, and remote from the roots. 
I have stated the above facts generally, now, because they tend to 
evince the importance of every healthy portion of the vegetable 
structure. Without particularizing further, I shall merely observe, 
that the sap undergoes a complete alteration after it has entered the 
cellular vessels of the leaves : that, in those organs it is converted by 
the agency of light and air, from an almost insipid fluid, into 
one possessing taste, odour, and colour ; and that this perfected 
sap is then propelled or attracted downward into the vessels of the 
liber or inner bark, and becomes the laborated substance termed 
cambium. This matter contains perhaps, all the molecules, or 
organized particles from which the alburnum or sap-wood of trees, 
and the parts analagous to it, of herbaceous plants are produced. 
The deposited sugary matter, spoken of by Mr. Knight, must be 
prepared in, and returned from, the leaves ; and as the inner bark 
is exterior in its position to that of the sap-wood through which the 
sap ascends, it is clear to a demonstration, that the proportion of 
prepared fluid derived from the former and blended with the latter, 
could be so only by a lateral or side-long progress. In this way 
then, a circulation may be said to exist ; for, there is, first, a posi- 
tive ascending current through the sap-wood ; second, a descending 
current from the leaves, through the bark, and to the roots; and 
third, a lateral or connecting current between the vessels of the bark 
and those of the alburnum. 
I do not attempt, in this article, to enter minutely upon an inquiry 
into the precise nature of the sap vessels — their structure, position, 
and functions ; for, it is one that properly belongs to the science of 
vegetable physiology : my chief design is to prove, beyond a doubt, 
the great importance of retaining in their integrity, every healthy 
portion of the vegetable organization ; and to evince that, by lop- 
ping off, or depriving a tree or plant of any one of its vessels of 
supply, or efficient organs of elaboration, a direct and positive act of 
mutilation is committed, injurious in proj^ortion to its extent, and 
ruinous if rashly persisted in. Such is the opinion of every impar- 
tial observer of nature, who views the operation of the pruner in 
connection with the philosophy of the vegetable structure. The 
real phytologist, when witnessing the fresh verdure produced by the 
amputations of the knife, is not deluded by mere appearances : he 
knows that nature has been severely taxed ; and that those new de- 
velopments are procured at the expense of much vital energy. 
