10 CHEMISTRY OF PLANTS. 



sorin, Salep, Lichen carragheen (Chondrus crispus) Gelin). This sub- 

 stance, when dry, is horny, or cartilaginous ; when moist, it swells up and 

 becomes gelatinous, and diffuses itself perfectly through cold pure water. 

 When pure it is clear, and is dissolved by (perhaps only diffused in) both 

 cold and hot water, and also in caustic alkalies ; it is, perhaps, chemically 

 changed in pure acids. It is insoluble in fixed and volatile oils, ether, 

 and alcohol, and is not coloured by iodine. It passes, on the one side, 

 through various transitionary bodies into cellulose (through the cell walls 

 of the Fucoidece), and into amyloid (through some kinds of horny al- 

 bumen), and on the other side into starch (through the jelly of the orchis 

 tubers), and, in many ways, into gum and sugar. None of these bodies 

 have been analysed, so far as I know, and reduced to chemical equivalents. 



Vegetable jelly forms the cell-walls of most Fucoidece, the albumen of 

 the C&salpinece, and, in part, the so-called horny albumen (Albumen 

 corneum). It is also, like gum, found in the contents of the cell. It 

 is especially abundant in the cells of the tubers of our indigenous Orchi- 

 dece and in the Cactacece, filling large individual cells, which at first often 

 exhibit upon their surface a granulated aspect : in the Cactacece they are 

 often distinguished by a vermiform twisted line. It is also seen, as a 

 secretion, in the gum-receptacles, especially in tragacanth ; and a part 

 also of the intercellular substance seems to belong to it. 



In the same way as in animal chemistry, we distinguish between 

 gelatinous substances and gelatine ; so does Kiitzing (Phycologia gene- 

 ralis, p. 32.) distinguish gelin from vegetable, which last, by boiling, 

 passes into the first. Vegetable jelly will also, by long boiling, pass into 

 mucilage (schleim). These three substances appear to me to be hydrated 

 states of a common basal principle. Kutzing's horny gelin (said to 

 contain nitrogen) and his gelacin (through hydrochloric acid coloured 

 verdigris-green) appear to be only gelin contaminated by foreign bodies. 

 At any rate, the experiment of determining the nitrogen which was 

 given off in the form of ammonia, during the combustion of an entire 

 plant, to be a constituent of a particular substance, is too coarse to be 

 admitted as of any worth at the present day. 



Whether pectin and pectic acid ought to be admitted under this head 

 appears, according to Mulder's experiments, doubtful.* He gives the 

 formula C 12, H 8, O 10. They appear to be more nearly related to 

 malic acid, and form, perhaps, transitionary bodies between the organic 

 acids and the indifferent secretions. The analyses, by Mulder, of the 

 carragheen moss (Chondrus crispus}, the mucilage of the quince and 

 the marshmallow, and of tragacanth gum, vary too much to allow of even 

 a common formula. The inquiry must not be disregarded, how the sepa- 

 ration of the various substances intimately mixed, as in the carragheen 

 moss and tragacanth gum, can be separated, so as to yield a pure substance 

 fitted for chemical analysis. That pectin belongs to the substances em- 

 ployed in thickening the cell-walls, is a fiction which no one microscopical 

 observation of ripe or unripe fruits, or of roots containing pectin, supports. 



4. Starch ( Amylum, Amiclon, Lichen -starch). When dry, it is toler- 

 ably hard, cracking between the fingers : when moist, somewhat gela- 

 tinous : dried from its solution, at first a trembling jelly, at last as brittle 

 as glass : when pure, constantly clear (even in lichens) : when perfectly 

 pure and fresh from the plant, gradually dissolving in water. This 

 solution may, perhaps, be regarded rather as a diffusion through water, 



* Poggendorf, Annalen, b. xlvi. (1838), p. 432. 



