138 VEGETABLE STRUCTURE. 
parts thro’ which it paffes are fo few, th^t we may with little difficulty 
trace it ; and yet as there are all the proper parts of the vegetable fabrick, 
we fhall, by fuch an examination, fee the whole fyftem of the nouriffi- 
ment of Plants. 
A QUANTITY of moifture is to be received from the earth and air, 
from the nouriffiment of the Plant ; and of this fuch a Part as is fit for 
that nouriffiment, is to be feparated from the refi, and conveyed to the 
feveral parts which are to grow ; the relf is to be difcharged. This is 
the intent of Nature : we have fcen the organs by which it is to be per- 
formed ; and we are here to trace the manner. 
The Fibres have Flefli, with Conic Clufters, and a Vafcular Series 
arifing from the fame parts in the body of the Root ; but they have alfo 
a Blea, and two Barks ; which tho’ they have like the reft arifen firft from 
the Flefti of the body of the Root, yet do not return into it again, as thole 
juft named, but purfue their plain courfe over it, from one extremity of 
the Plant to the other. This is the diftindtion of thofe feparate arrange- 
ments of parts ; and the courfe of their Juices appears to be this. 
The outer Bark of the Root runs down tlie Fibres, and up to the crown 
of the Bud, where it terminates in a kind of Films. This Bark, while 
the Fibres are furrounded with the moifture of the earth, receives that 
moifture thro’ its fpungy furface, and into all its Vefl'els. Thefe are fo 
many extremely minute tubes, up which the fluid afeends by the attradlioii 
of their fides ; and in this afeent it is greatly affifted by that compreffion 
'and dilatation which arifes from the continual change of temperature in the 
air. The courfe of thefe V^effels is over the body of the Root, and up to 
the fummit of thofe Films wherein this outer Bark terminates. They are 
fpungy here as elfewhere, and the Juices they contain can eafily pafs in part 
thro’ their furface. 
During the warm hours of the day there is a conftant evaporation of 
part of this Juice of the outer Bark from the Films ; and by this means 
the Veflrls are often emptied, faftcr than they can be fupplied by the Fibres.. 
On the other hand, when the heat of the day is over, and this evapora- 
tion ceafes, a new operation obtains in the fame parts : the air grows damp, 
and the fpungy lurfaces of thofe Veflfels which are expofed to it, can as 
eafily imbibe as they could before perfpirc : therefore a great quantity of 
moifture is, during thefe hours of the night, taken in at the furfaces above 
ground, and makes its way, in fome meafure, down the Veflfels. 
This feems to be all the abfolute motion of the Juices in the Veflels of 
the Bark ; and if fo, it has been very idly fuppofed to be circulatory r yet 
as 
