SECT. II. COMPOSITE ORGANS. '215 



nizable to the sense of sight, though the detail of 

 the process is often so very minute as to escape even 

 the nicest observation. All,, then, that can be said on 

 the subject is merely that the tubes, however formed, 

 do, by virtue of the agency of the vital principle 

 operating on the proper juice, always make their 

 appearance at last in an uniform and determinate 

 manner, according to the tribe or species to which 

 the plant belongs, uniting and coalescing so as to 

 form either a circular layer investing the pith, as in 

 woody plants ; or a number of divergent layers in- 

 tersecting the pith, as in some herbaceous plants ; 

 or bundles of longitudinal and woody fibre inter- 

 spersed throughout the pith, as in others ; though 

 in some of the less perfect plants no longitudinal 

 fibres are at all discernible, and consequently 

 no part analogous to wood. 



In the same manner we may account for the form- And bark, 

 ation of the layer of bark, either by supposing 

 that it is merely the developement of some original 

 elements existing in the embryo, or that it is gene- 

 rated by means of the agency of the vital principle 

 in the process of vegetation and out of the proper 

 juice, so as to form an exterior layer distinct in its 

 character and properties, and separate or easily 

 separable from the wood or interior part of the 

 plant. 



Such is a slight sketch of the process of the de^ 

 velopement of the elementary and composite organs 

 of annuals, or of perennials of a year's growth. 



