THE INNER ORGANIZATION OP TREES. 37 



CHAPTER III. 



THE INNER ORGANIZATION OF TREES, OR A DESCRIPTION OF THE 

 ANATOMY AND PHYSIOLOGY OF THE DIFFERENT SPECIES OF 

 CELLS WHICH ENTER INTO THE COMPOSITION OF THEIR TISSUES. 



IF we wish to recognize the law according to which the 

 tree is built up out of its parts as a compound harmonious 

 whole, we must first resolve the representation of the whole 

 into that unit which lies at the foundation of its super- 

 structure. This we have already done, to some extent, in 

 the two previous chapters. Taking the tree, in the most 

 extended signification of the term, as a separate individual 

 or unit with reference to a forest, we have shown that this 

 individual tree consists of a number of individual plants of 

 a highly composite character called branches, which differ 

 from the entire tree itself only in the smaller scale on 

 which they are constructed, and which actually prefigure 

 the amount of growth of that tree at an earlier stage of its 

 life. These branches are formed by a union of yet simpler 

 individuals called shoots, and the shoots themselves are 

 built up by phytons or leaves, individuals or units which 

 rank still lower in the series. In this manner we have 

 been lead to the leaf at the fundamental organ in the 

 building up of the tree-form. 



But this analysis may be carried much further. It may 

 be applied to the inner organization of the tree. Thus the 

 axis or stem separates into two distinct systems the bark 

 and the wood, as the two highest units of its anatomical 

 composition. Each of these systems again resolves itself 

 into a repetition of single annual layers. If we examine 

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

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



