FORMATION OF PROPER JUICE. 207 



posed of the same elements, in the same proportions, from what- 

 ever tree it is taken, provided it be cleared from those substances 

 which are deposited within it, for the purpose of affording it 

 additional strength. But when we look at the immense variety 

 of products which the Vegetable kingdom supplies, varying no 

 less in properties than in appearance, we are lost in wonder at 

 the marvellous nature of those processes, in which a difference, 

 undiscoverable by all our most refined means of research, shall 

 be productive of such a number of widely- different results. And 

 at the same time the reflecting mind cannot forget, that these 

 results are all of a kind most valuable to Man, furnishing him 

 with the necessaries, the comforts, and the luxuries of life, 

 support in health, medicine in disease, and the materials of great 

 part of his clothing, his books, and various articles which minister 

 to his mental and moral improvement. 



327. These substances may be distinguished under two 

 classes ; the nutritive products, adapted to supply the materials 

 of increase to the tissues themselves ; and the special secretions, 

 which are for the most part contained or stored up in them. 

 The former are common to all plants ; of the latter different 

 kinds exist in the various tribes. 



328. Of the nutritive products, which are carried by the 

 descending sap to all parts of the structure, (as are those of a 

 similar nature contained in the blood of animals,) the principal 

 is Gum. This is found in the bark and wood of all plants ; and 

 is present in such abundance in several, which are called Gum- 

 trees, as to flow in plenty from the bark when wounded, or when 

 its surface cracks. Of these trees, most belong to the Acacia 

 tribe ; and it is in warm climates only, that the formation of this 

 product is so abundant, as to make the collection of it desirable. 

 Various modifications of this principle exist in different vege- 

 tables ; but they may all be regarded as combinations of pure 

 gum with other substances. Gum Arabic is one of its simplest 

 forms ; this is really brought from Arabia, where it is annually 

 collected in the Acacia forests, at the end of November. A large 

 quantity is imported into this country, on account of its extensive 

 use in calico-printing and other arts. It is a highly nutritious 



