CHAPTER VIII. 



OF THE MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS. 



222. Mementary Tissues. — In passing from the Cryptogamie 

 division of the Vegetable Kingdom, to that larger and more 

 ostensibly important province which includes the Flowering 

 Plants, we do not meet with so wide a departure from those 

 simple types of structure we have already considered, as the 

 great diiferences in general aspect and external conformation 

 might naturally lead us to expect. For a very large proportion 

 of the fabric of even the most elaborately formed Tree, is made 

 up of components of the very same kind M'ith those which con- 

 stitute the entire organisms of the simplest Cryptogamia; and 

 that proportion always includes the parts most actively con- 

 cerned in the performance of the vegetative functions. For 

 although the stems, branches, and roots, of trees and shrubs, are 

 principally composed of woody tissue, such as we do not meet 

 with in any but the highest Cryptogamia, yet the special office 

 of this is to aiford mechanical support ; when it is once formed, 

 it takes no further share in the vital economy, than to serve for 

 the conveyance of fluid from the roots, upwards through the stem 

 and branches, to the leaves; and even in these organs, not only 

 the pith and the bark, with the "medullary rays" which serve to 

 connect them, but that " cambium-layer" intervening between 

 the bark and the wood (§ 240), in which the periodical formation 

 of the new layers both of bark and wood takes place, are com- 

 posed of cellular substance. This tissue is found, in fact, 

 wherever growth is taking place ; as, for example, in the spon- 

 gioles or growing points of the root-fibres, in the leaf-buds and 

 leaves, and in the flower-buds and sexual parts of the flower ; it 

 is only when these organs attain an advanced stage of develop- 

 ment, that woody structure is found in them, — its purpose (as in 

 the stem) being merely to give support to their softer textures ; 

 and the small proportion of their substance which it forms, being 

 at once seen in those beautiful skeletons, which, by a little skill 

 and perseverance, may be made of leaves, flowers, and certain 

 fruits. All the softer and more pulpy tissue of these organs is 

 composed of cells more or less compactly aggregated together, 



