R6 CHEMICAL CO>-STITUTION OF VEGETABLES. 



ments, at a temperature no higher than 20° cent. (68° Fahr.) a quan- 

 tity of starch, at the end of twenty-four hours, was converted into 

 sirup, which yielded 77 per cent, of saccharine matter.* 



Pure dextrine. M. Payen freed dextrine from the sugar which 

 usually accompanies it by precipitating a sirup of fecula previously 

 dissolved in dilute alcohol, by means of alcohol nearly free from wa- 

 ter. Dextrine well dried, and reduced to powder, has a specific 

 gravity of 1.51. The specific gravity of pure starch is 1.51, that ol 

 the sugar of starch 1.61.t 



M. Payen found dextrine dried at a temperature of 212' Fahr. to 

 consist of — 



Carbon 44.3 



Hydrogen 6.0 



Oxygen 49.7 



100.0} 



a composition identical with that of starch. 



We have seen that water, acidulated with sulphuric acid, trans- 

 forms starch into sugar ; and that in this respect, the acid acts pre- 

 cisely in the same way as malted barley, like which, the acid first 

 causes the fecula to pass into the state of dextrine : by checking the 

 reaction at the proper moment, this substance may thus be obtained, 

 as was shown by Messrs. Biot and Persozj^ When starch, for in- 

 stance, is triturated with concentrated sulphuric acid, if the mixture 

 be diluted with half its volume of water, and be left at rest for an 

 hour, alcohol will throw down almost the whole of the starch employ- 

 ed in the state of dextrine. 



M. Payen has remarked that starch is never met with in the vege- 

 table tissues while in the rudimentary state ; the sponfjioles, the radi- 

 cles, the foliaceous buds, the interior of the ovules, contain none of it. 

 Nor is starch found in the epidermis, nor in the primary cells of the 

 subjacent tissues. This proximate principle seems to be exclu- 

 ded I'rom those parts of vegetables that are more directly exposed to 

 atmospheric influences : it is only met at a certain depth ; and the 

 globules which constitute starch increase in number and in size in 

 the cells most remote from the surface. The subterraneous organs 

 of plants, — certain bulbs, most tubers, abound in amylaceous matter. 

 It migiit be maintaineil that light modified this substance, at the very 

 moment that it was subjected to the vital influence, and that it was 

 only preserved in the dark. 



On the globules of some species of f<ecula there is found a point 

 or hilum, which, according to some observers, serves to fix them to 

 the parietes of the cells which enclose them. It ot'ten happens, 

 however, that no hilum can be distinguished, even by the help of the 

 most powerful microscopes ; to render it apparent, recourse must bo 

 had to desiccation, which, by causing the globular mass to shrink, 

 allows the part carrying the hilum to project, by reason of its 



• Gu6rin, Annalcs de Chiiuio, t. Ix. p. 4'2, 2e s6ric. 



t Pnyen, M^iiiniros citts. p. 169. I Idem, p. 157. 



% Blot nnd IVrsoz. .\nnales de riiiinio et dc Physique, t 111. p. 73, Se sAlto. 



