VEGETABLE PRODUCTS. 



J37 



tity auJ quality. The terminal or smallor 

 branches first fade and decay, and then the larger 

 branches, together with the trunk and root. The 

 vegetative energies gradually decline, and at last 

 totally cease. At last the whole solid mass of 

 the plant, acted on by the sun-ounding elements, 

 moulders down and mingles with the dust from 

 which it originally sprang. Such is at last the 

 fate of the aged oak, as well as the fragil weed; 

 each has its allotted span; but in the present 

 state of physiological knowledge, it would be 

 utterly vain to attempt a solution of the mys- 

 terious cause. 



CHAP. XXI. 



VEGETABLE PRODUCTS. 



The simple or elementary substances which 

 enter into the composition of all vegetables, are, 

 as we have already shown, confined to a very 

 small number. Oxygen, hydrogen, nitrogen, 

 carbon, lime, silex, alumina, magnesia, potash, 

 soda, iron, forming the greater part of the list. 

 Plants, however, are endowed with the powers 

 of assimilating and combining these various sub- 

 stances into compounds, assuming various forms 

 and properties. The chief of these vegetable 

 compounds are gum, sugar, farina or starch, 

 gluten, albumen, fibrina, extract, tannin, colour- 

 ing matter, bitter principle, narcotic principle, 

 alcohol, acids, oils, wax, resins, gum resins, 

 balsams, camphor, caoutchouc, cork, lignin or 

 woody fibre, sap, proper juice ; while the simple 

 or uncombined products are carbon or charcoal, 

 the mineral alkalies, earthy and metallic oxides. 



Gum. This is a substance which flows spon- 

 taneously from the bark and leaves of many 

 plants. It is at first a viscid, transparent, and 

 tasteless fluid ; and, on exposure to the atmos- 

 phere, gradually solidifies into a mass. Gum 

 is produced abundantly from many of our frait 

 trees, especially those which have stone kernels, 

 as the cherry and plum. It flows from fissures 

 in the baric, and sometimes from the fruit itself. 

 Some plants do not discharge it spontaneously; 

 but from those it may be extracted by macera- 

 tion in water. There are several varieties of 

 gum, known under the name of gum Arabic, 

 gum tragacanth, cherry tree gum, and mucilage. 



Gum, Arabic is obtained from the mimosa 

 nilotica, a native of the interior of Africa, and of 

 Arabia, from whence it has obtained its name. 

 Gum Senegal, an exactly similar gum, is pro- 

 cured from acacia vereh. It comes to this country 

 in irregular globules, or masses ; is hard, brittle, 

 and when pure almost colourless, or of a slight 

 straw-colour, and transparent. It readily dis- 



solves in water, forming an adhesive and emol- 

 lient mucilage; and if left exposed to the air 

 will again soon form into a hard mass, in the 

 evaporation of the water. It is insoluble in alco- 

 hol. 



By chemical analysis, 100 parts of gum Arabic 

 contain the following elementary matters : 



Carbon 42.23 



Oxygen 50.84 



Hydrogen 6.93 



Saline and earthy matter, a small quantity. 



Gum tragacanth. This substance is obtained 

 from astragalus tragacantha, a thorny shrub, 

 which grows abundantly in the islands of the 

 Levant. The gum exudes spontaneously from 

 the stem and branches. In appearance, it re- 

 sembles gum Arabic, and is similar to it in its 

 other properties, though less transparent, and less 

 soluble in water. It comes to this country in 

 thin twisted plates or cakes. 



Cherry tree gum, is obtained from the prunus 

 avium, and other similar species, and indeed, 

 from all trees bearing stone fruits, from the bark 

 of which it spontaneously flows. It is in all 

 essential points of similar properties to the fore- 

 going gums ; but rather more easily melted by 

 heat. This gum contains a peculiar substance, 

 -called cerasin. Mucilage is found in the roots 

 and leaves of bulbous rooted and succulent 

 plants, such as the bulbs of the hyacinth, and 

 leaves of the marshmallow, {malva st/lvestris;) 

 it is found also abundantly i-n lintseed, and in 

 several other oily seeds. It may be extracted 

 also from many of the lichens by maceration 

 in water, and separated by the addition of sul- 

 phuric acid. 



Gum and mucilage, though insipid to the 

 taste, contain highly nutritive qualities and form 

 a useful diet in some kinds of diseases and par- 

 ticular states of the digestive organs. Gums are 

 also externally used in the arts, particularly in 

 calico printing, in which the printers use them 

 to give consistency to their colours, and to prevent 

 their spreading on the cloth. Gums are used as 

 convenient adhesive fluids for pasting substances 

 together. A simple solution of gum in water, 

 with tlie addition of a little spirit of lavender, 

 to prevent the acetous fermentation, is the most 

 convenient for all purposes of this kind. Gum 

 also gives thickness to ink, and promotes the 

 intimate mixture of its particles. In medicine 

 it is also used extensively. 



Sugar. This important article is found in the 

 juices of a great many vegetables, but in gi-eatest 

 abundance in the sugar cane, {armida sacchari- 

 fera,) from which the sugar of commerce u 

 manufactured. This cane, when it has arrived 

 at its proper state of maturity, is found to be 

 fuU of a sweet juice. In this state it is taken 

 and bmised between the rollers of a mill, the 



