38 THE INNER ORGANIZATION OF TREES. 



one of these layers with a microscope, we shall find it also 

 to be a compound, and that it can be resolved into indi- 

 viduals having distinct peculiarities of form and function, 

 called cells. We have now arrived at the lowest and 

 simplest individual or elementary organ, the CELL. 



By the aid of Chemistry we can descend however, another 

 step, and can resolve the cell into its original elements 

 of sugar, water, salts, and protein compounds, and these 

 again into their ultimate elements, Oxygen, Hydrogen, Car- 

 bon, and Nitrogen elements into which this grand, living, 

 and wondrous architecture of Nature is at last resolved, 

 when it has passed through all the phases of its life, as its 

 defoliated form slowly disappears from the landscape. 



Now as all clear and correct views of the anatomy and 

 physiology of trees must be based on a knowledge of their 

 minute structure, before proceeding further we shall give 

 some account of these simple elementary cells ; for by this 

 means we shall be able to explain more satisfactorily cer- 

 tain superficial and very obvious appearances of their bark 

 and wood, and thus advance another step in the elucidation 

 of the philosophy of their growth. It is indeed necessary 

 to the perfection of this picture of the building-up of the 

 tree, that we should begin with the simplest building stone, 

 the CELL, which is the basis of the whole living super- 

 structure, and to which we have been led by the above 

 analysis. 



If we examine the transverse section of the stem of a 

 young beech-tree, we shall find it to be composed of a number 

 of concentrical and alnost circular beds or layers of wood, 

 ensheathing one another about a common centre, which is 

 occupied by a canal of medulla or pith, and the whole of 

 which is covered by the bark formed on the exterior of the 

 stem. Even without a microscope, there is no difficulty in 

 distinguishing the bark, the wood, and the pith, and thus in 

 ascertaining the fact that the stem is composed of three 

 separate and distinct systems; but when we examine a thin 

 cross-section of one of the newly-developed shoots with the 

 microscope, we obtain a far more correct view of its 



