CHAPTER II. 



WOODY AND VASCULAR TISSUE. 



25. It has been shown (4) that every plant consists of a 

 series of cells aggregated together, having a certain arrange- 

 ment, and developing into a certain regular form, according 

 to fixed natural laws. The cells thus aggregated together con- 

 stitute what botanists call a tissue, which tissue, according to 

 the forms which the cells assume, is designated as cellular, 

 vascular, and woody tissue. These are the three leading 

 forms; but, in the study of nature, we must accustom our- 

 selves to consider that there are transition forms, and never 

 to believe that one and the same type remains unchanged. 

 With this qualifying remark, we can now very properly in- 

 vestigate, 



26. Woody tissue, or, as it is termed by some writers, fibrous 

 tissue, or Pleurenchyma (rtXtupo a rib, and x'^fia anything 

 eiFused or spread out). Fig. 6, consists of vesicles of cellular 

 tissue drawn out into fusiform tubes of extreme tenuity and 

 toughness, which lie close together and overlap each other at 

 their tapering extremities, so that they are, as it were, spliced 

 together. These tubes, united together in bundles, constitute 

 the wood of the stem, and form those long coarse fibres which 

 stretch through the plant lengthwise. Issuing from the side 

 of the stem in distinct fasciculi or bundles, this woody fibre 



