SECT. IV. DECOMPOSITE ORGANS. 245 



of the alburnum and bark. Their existence is as- 

 sumed but not accounted for. We are told, indeed, 

 that the tubes of the alburnum arc not discoverable 

 at a very early period of vegetation, as coloured in- 

 fusions are not absorbed by the plant till it is some 

 weeks old, even when part of the root is cut off, at 

 least in the case of the Horse-chesnut,* though 

 they begin to be discoverable soon after that period. 

 But we are not favoured even with a conjecture with 

 regard to the probability of their actual origin ; 

 whether as being wholly generated in the progress 

 of vegetation, or as being merely developed by the 

 intro-susception of nutriment into some primordial 

 and duly organized element pre existing in the 

 embryo. 



SECTION IV. 



Decomposite Organs. 



To the above brief sketch of the agency of the 

 vital principle in the generation or growth of the 

 elementary and composite organs, there now re- 

 mains to be added that of the progress and mode of 

 the growth of the decomposite organs, or organs im- 

 mediately constituting the plant, as finishing the 

 process of the vegetable developement. This will 

 include the phenomena of the ultimate develope- 

 ment of the root, stem, branch, bud, leaf, flower, 

 and fruit. 



* Phil. Trans. 1806. 



