3^ On the Anatomy of Vegetables. 



thefe -threads arc furrounded with a foft, elaftic, fpongy Jub- 

 ilance, eafily torn, and generally whitifh, which is called the 

 pith, and to which 1 flia.ll give the name of parendynie, that 

 it may not be confounded with the pith of the dicotyledon 

 plants. The wood of the latter, lying always under the bark, 

 is not divided into diftincl threads \ it generally forms a cy- 

 linder, in the centre of which is placed the pith, as in a cafe. 

 Some plants, however, evidently furniihed with two cotyle- 

 dons, exhibit ligneous filaments fimilar to thofe of the mo- 

 nocotyledons, running along the whole length of the medul- 

 lary canal : butthefe are exceptions which do not deilroy the 

 general rule. 



In trees or (limbs with two cotyledons there are almoft 

 always obferved diflincl lines of the wood, which proceed 

 from the pith, traverfe the ligneous cylinder, and end at the 

 bark. They appear on the tranfverfal feclion of the trunk, 

 ftem, branches, and twigs, like the hour- lines of a dial. 

 They are called the medullary radii. They feldom fhow 

 themfelves in the items of the dicotyledon herbs, and do not 

 e*ift in the monocotyledons either herbaceous or ligneous. 



In the leaves, flowers, pericarpia, &x. there are found alfo 

 parts of greater or lefs foftnefs, and greater or lefs hardnefs, 

 the fubftance of which appears to be fimilar to the bark, pith, 

 or wood. 



Such are the different parts which vegetables exhibit to 

 the naked eye. We mnft now examine the elementary or- 

 gans which enter into their compofition. 



Chap. II. 



Of the Me?nbrano7/s Tiffue. 



Vegetables are compofed of a membranous tifTue, which 

 varies in its form and confidence, not only in the different 

 fpecies, but even in the fame individual. I mail not here 

 examine whether the membranes are compofed of organic, 

 fibres, ranged clofe to each other and united by a gluten, as 

 fome authors alTert. This fuppofition is fufceptible neither 

 of ftrict demonltration, nor a formal refutation ; it is one of 

 thofe fyftcms which amule the mind when refearch becomes 

 fruitlefs. I fhall content myfelf with fiating, that, whatever 

 may have been the peifeverance of my obfervations, I never 

 obferved real fibres in vegetables; the filaments to which 

 that name has been given are only membranes, which tear 

 into longitudinal (tripes: fuch were the delicate filaments 

 which L'uhamel feparated fiom a bit of wood which he ob- 

 ferved through the microfcope. 



The membranous tiflue, though continued in all its parts, 

 4 form* 



