CHAPTER VIII. 



OF THE MICROSCOPIC STRUCTURE OP PHANEROGAMIC PLANTS. 



283. Elementary Tissues. — In passing from the Cryptogamic 

 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 differences 

 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 

 vei*y same kind with those which constitute the entire organisms of 

 the simplest Cryptogamia ; and that proportion always includes the 

 parts most actively concerned 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 afford 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 ' Medullaiy Rays, ' which 

 serve to connect them, but that ' Cambium-layer ' intervening 

 between the bark and the wood (§ 303) in which the periodical 

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

 composed of Cellular substance. This tissue is found, in fact, 

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

 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 development, 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 per- 

 severance, 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, and having 

 forms that approximate more or less closely to the globular or 

 ovoidal, which may be considered as their original type. 



