372 CONSERVATIVE ORGANS. [LECT. VII. 



being a distinct organ in every stage of its ex- 

 istence. 



To enter at present upon the explanation of 

 the formation of the pith, would be anticipating 

 our inquiries into the general theory of vegetation, 

 a part of our subject for the discussion of which 

 we are not yet fully prepared. Regarding, how- 

 ever, the mere mechanical causes which possibly 

 operate in producing the hexagonal form of the 

 cells, I may remark that, if the ,gelatinons pulp, 

 which constitutes the earliest state of the pith, as- 

 sumes the form of globules as the first effect which 

 the operation of the vital organizing influence pro- 

 duces on it ; it is easy to conceive that, from the 

 individual inflation of these occasioning them to 

 press in every direction upon one another, within a 

 certain limit, each globule will necessarily acquire 

 an hexagonal form. In this state the flat surfaces 

 of the enclosing membrane of each globule which 

 are in immediate contact, uniting and acquiring 

 firmness, while the contained fluid is dissipated 

 and air admitted, the cavity it occupied will re- 

 main as an hexagonal cell ; and of such is the dry 

 pith constituted. To produce this effect, how- 

 ever, the following circumstances are necessary: 

 1. The membrane which divides each cell from 

 those adjoining it, must be double, which Link * 



* Secunda Dissert, in Homer's Collect. Bot. fascic. i. p. 163. 



