INTERNAL STRUCTURE OF PLANTS. 
13 
position Chimique du Tissu Propre des Vegetaux,” in the An- 
nales des Sciences Naturelles, vol. xiii. p. 305. 
The reporters are, Dumas, Pelouze, and Ad. Brongniart. 
Payen caused caustic potass in a heated state, then iodine, 
and occasionally sulphuric acid, to act upon different vegetable 
substances, and observed, that the original membrane, which 
constitutes the integuments of the cells, remained without any 
change. He found, on the other hand, that the deposits on 
this membrane converted themselves into a substance under 
the action of potass, which, on application of iodine, assumed 
a violet colour (blue-violet) ; and that, finally, a part of these 
new products, which he terms secondary ones, were converted 
by the same influences into another substance, which assumes 
an orange colour on the application of iodine. It appears, 
further, from his numerous analyses, that the vegetable tissues, 
both of the Plianerogamia and the Cryptogamia, by the con- 
tinued solution of all foreign substances, which have either 
been deposited in their cavities, or on the membranes them- 
selves, may be traced to a substance (cellulose), which con- 
stitutes the original walls of the cells of the cellular tissue, of 
the woody tissue, and of the vessels, which has the same com- 
position as starch, and is only distinguished by its aggregated 
state, through means of which it exhibits a stronger degree of 
resistance to chemical influences. The similarity of the cel- 
lulose and of starch, with regard to elementary composition, 
the transformation of both substances into dextrine and sugar, 
would, indeed, in themselves, lead us to suppose, that inter- 
mediate states exist. In fact, the author observed, that the 
membrane of the Cetraria islandica, when properly cleansed, 
assumes a blue colour on the application of iodine, and is 
dissolved like starch in soda. The thick walls of the cells in 
the albumen of Pliytelephas and Braccena likewise, when 
properly cleansed, assume a blue colour on the application of 
iodine, but resist solution longer than the cellular substance 
of the Lichenes, The reporters add : — Cells of woody tissue, 
when freed from all foreign substances, so as no longer to 
assume a black colour on the application of muriatic acid, 
and of weak sulphuric acid ; nor an orange colour, on the 
405 
