COMPOSITION, SAP, ETC. 21 



some other trees of the tropics, possess remarkable properties. 

 The juice of the common milk weed is said to be similar to that of 

 the India rubber plant. The valuable properties of these substances 

 will be treated in the second part of this work, with those of the fol- 

 lowing. 



The. second class of proximate principles are composed of the ulti- 

 mate elements we have mentioned with nitrogen. Such are opium, 

 the narcotic principle of the poppy ; hematine, the coloring principle 

 of Campeachy wood ; indigo, from species of the indigo plant , gluten, 

 from the cotyledons of leguminous plants, as beans and peas; also 

 from the albumen of wheat, rye, etc., when separated from the starch. 

 Jelly is the juice of suculent fruits, as apples, quinces, currants, etc. 

 The coloring principle of plants gives to them their green color, by the 

 aid of light. It is changed, as in autumn, by the formation of an acid. 

 Thus a drop of an acid on the green part will turn it to a brown. 

 The coloring matter of some plants has never been obtained separate 

 from the plant, as in logwood, and saffron. The red coloring of fruit 

 is produced by the combination of an acid with a blue coloring princi- 

 ple, as an acid will do with all vegetable blues ; this is deeper in pro- 

 portion to the quantity of acid. An acid with iron is the common 

 coloring principle of flowers. 



The composition of the sap of plants is from the before-mentioned 

 elements and water holding in solution the earths and their metalic 

 bases, alkaline, salts, etc., with vegetable and animal substances. It 

 is not obtained pure, being always mixed with the proximate principles 

 before-mentioned ; and it differs in plants in proportion to those prin- 

 ciples. The power or property of a plant to secrete one kind of sub- 

 stance and not another depends on their constitutional peculiarities, 

 as with races of men in the formation of their different colors. Water 

 is always a predominant constituent of the sap of plants. An analysis 

 of the sap of the elm gives water, volatile matter, acetate of potash, 

 carbonate of lime, sulphate of potash and vegetable matter; of the 

 beech, water, acetate of lime, acetate of potash, gallic acid, tannin, 

 mucous extract, acetate of alumine, etc. These show the differences 

 in the elements of the sap ; they also differ materially in their pro- 

 portions. The odor, taste, nutritive and medicinal qualities, color, 

 etc., are all the result of these elements, variously combined. The 

 elements are the same in substances of very different character, solids 

 as well as fluids, but their mode of combination may form vinegar or 

 a liquid in one, and sugar or a solid in another. By knowing these 

 elements and their proportions, similar substances may be produced by 

 the chemist, but not the form and organization of the plant, these 

 being alone the work of nature in conformity with laws established 

 jy Supreme Wisdom. 



