38 THE INNER ORGANIZATION OF TREES. 



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 num- 

 ber of coneentrical and almost 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 diffi- 

 culty 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 

 anatomical structure. We see that the bark and pith are 

 composed of a number of bladder-like vesicles or cells of a 



