24S THE FLUID COMPONENTS OF PLANTS. 



to be suspended in water, and taken in by the absorb- 

 ent vessels of the roots. i his is in some degree 

 proved by the effect of change of situation on plants 

 which naturally grow near the sea ; for most of these, 

 when burnt, yield soda; but, when they are removed 

 from the sea-shore, and cultivated in an inland situa- 

 tion, potash instead of soda is procured from their 

 ashes. Still, the siliceous epidermis of Grasses and 

 Canes, and the flinty liquor sometimes found in the culms 

 of the latter, can scarcely be produced in any other 

 manner than by proper vegetable assimilation deposi- 

 ting silex from its unknown elements. As the sap 

 undergoes the same exposure to the air and light in 

 all plants, and one product only can be formed in each 

 plant by this exposure, the difference of the proper 

 juice in different plants, is a strong argument in favor 

 of the existence of vegetable glands, independent of 

 the undeniable proof afforded by the formation of the 

 very different products which are deposited in different 

 parts of the same plant. Unless there were glandu- 

 lar organs, one product only could be produced in 

 each plant by the function of the leaves, and the ac- 

 tion of light and of air on the sap. The secretions 

 of plants formed from the proper juice are very nume- 

 rous, and known under the names of gum, fecida or 

 starch, sugar, gluten, albumen, gelatin, caoutchouc or 

 Indian rubber, ivax, fixed oil, volatile oil, camphor, 

 resin, gum resin, balsam, extract, tannin, acids, aroma, 

 the bitter, the acrid, and the narcotic principles, and lig- 

 neous fibre. These are found in different parts of plants 

 without any uniformity of distribution ; and although 

 so numerous and different from each other in their 

 sensible qualities and chemical properties, yet are they 

 all composed of different modifications of the same 

 elements, Carbon, Hydrogen, and Oxygen. Thus 

 100 parts of gum, according to the experiments of 

 Gay Lussac and Thenard, consist of 



