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CHAPTER 1. 
ELEMENTARY ORGANS. 
The general properties of the elementary organs are elasticity^ 
extensibility ^contractibility^^Yid permeability to fluids or gaseous 
matter. The first gives plants the power of bending to the 
breeze, and of swaying backwards and forwards without break- 
ing. The second enables them to develope with great rapidity 
when it is necessary for them to do so, and also to give way to 
pressure without tearing. The third causes parts that have 
been overstrained to recover their natural dimensions when 
the straining power is removed, and it permits the mouths of 
wounded vessels to close up so as to prevent the loss of their 
contents. The fourth secures the free communication of the 
fluids through every part of a plant which is not choked up 
with earthy matter. 
The special properties of the elementary organs must be 
considered separately. 
That of these the cellular tissue is the most important 
is apparent by its being the only one of the elementary organs 
that is uniformly present in plants ; and by its being the chief 
constituent of all those compound organs that are most essen- 
tial to the preservation of species. 
It transmits fluids in all directions. In most cellular plants 
no other tissue exists, and yet in them a circulation of sap takes 
place ; it constitutes the whole of the medullary rays, convey- 
ing the elaborated juices from the bark towards the centre of 
the stem; all the parenchyma in which the sap is diffused 
upon entering the leaf, and by which it is exposed to evapor- 
ation, light, and atmospheric action, consists of cellular tissue ; 
nearly all the bark in which the descending current of the 
sap takes place is also composed of it ; and in endogenous 
plants, where no bark exists, there appears to be no other 
