BOOK I. SIMPLE PRODUCTS OF PLANTS. 157 



of salsola contain also a considerable quantity. The oxide of manganese was first detected in the ashes of 

 vegetables by Scheele, and afterwards found by Proust in the ashos of the pine, calendula, vine, green oak, 

 and fig-tree. Beccher, Kunckel, and Sage, together with some other chemists, contend also for the exist- 

 ence of gold in the ashes of certain plants ; but the very minute portion which they found, seems more 

 likely to have proceeded from the lead employed in the process than from the ashes of the plant. It has 

 been observed by Saussure, that the proportion of the oxides of iron and of manganese augments in the 

 ashes of plants as their vegetation advances. The leaves of trees furnish more of these principles in autumn 

 than in spring. It is so also with annual plants. Seeds contain metals in less abundance than the stem ; 

 and if plants are washed in water, the proportions of their metallic oxides is augmented. 



712. Such are the principal ingredients that enter into the vegetable composition. They are indeed nu- 

 merous, though some of tnem, such as the metallic oxides, occur in such small proportions as to render it 

 doubtful whether they are in reality vegetable productions or no. The same thing may be said of some of 

 the other ingredients that have been found in the ashes of plants, which it is probable they have absorbed 

 ready formed by the root, and deposited unaltered, so that they can scarcely be at all regarded as being the 

 genuine products of vegetation. 



713. Other substances. Besides the substances above enumerated, there are also several others that have 

 been supposed to constitute distinct and peculiar genera of vegetable productions, and which might have 

 been introduced under such a character; such as the mucus, jelly, sarcocol, asparagin, inulin, and ulmin, 

 of Ur. Thomson, as described in his well known System of Chemistry ; but as there seems to be some dif- 

 ference of opinion among chemists with regard to them, and a belief entertained that they are but vari- 

 eties of one or other of the foregoing ingredients, it is sufficient for the purposes of this work to have 

 merely mentioned their names. Several other substances of a distinct and peculiar character have been 

 suspected to exist in vegetable productions : such as the febrifuge principle of Seguin, as discovering itself 

 in Peruvian bark'; the principle of causticity or acridity of Senebier, as discovering itself in the roots of 

 ranunculus bulbosus, scilla maritima, bryonia alba, and arum maculatum, in the leaves of digitalis pur- 

 purea, in the bark of daphne mezereon, and in the juice of the spurges : to which may be added the fluid 

 secreted from the sting of the common nettle, the poisons inherent in some plants, and the medical virtues 

 inherent in others ; together with such peculiar principles as may be presumed to exist in such regions of 

 the vegetable kingdom as remain yet unexplored. The important discoveries which have already resulted 

 from the chemical analysis of vegetable substances encourage the hope that further discoveries will be the 

 result of further experiment ; and from the zeal and ability of such chemists as are now directing their 

 attention to the subject, every thing is to be expected. 



SECT. II. Simple Products. 



714. From the above analysis of the vegetable subject, it is evident, that the compound 

 ingredients of vegetables are all ultimately reducible to a very few constituent and uncom- 

 pounded elements; and that the most essential of such compounds consist of carbon, 

 oxygen, and hydrogen, merely ; though others contain also a small proportion of nitrogen, 

 said to be found only in cruciform plants. The remaining elementary principles which 

 plants have been found to contain, although they may be necessary in the vegetable 

 economy, yet they are by no means principles of the first importance, as occurring only in 

 small proportions, and being dependent in a great measure on soil and situation ; whereas 

 the elements of carbon, oxygen, and hydrogen, form as it were the very essence of the 

 vegetable subject, and constitute by their modifications the peculiar character of the pro- 

 perties of the plant. This is conspicuously exemplified in the result of the investigations 

 of Gay Lussac, and Thenard, who have deduced from a series of the most minute and 

 delicate experiments the three following propositions, which they have dignified by the 

 name of Laws of Vegetable Nature (Traitede Chem. Element, torn. iii. chap, iii.) : 1st, 

 Vegetable substances are always acid when the oxygen they contain is to the hydrogen in 

 a greater proportion than in water ; 2dly, Vegetable substances are always resinous, or 

 oily, or spirituous, when the oxygen they contain is to the hydrogen in a smaller propor- 

 tion than in water ; Sdly, Vegetable substances are neither acid nor resinous, but sac- 

 charine or mucilaginous, or analogous to woody fibre or starch, when the oxygen and 

 hydrogen they contain are in the same proportion as in water. Such is a brief sketch of 

 the vegetable analysis : but if the reader, not being already an adept, wishes to descend 

 into the detail of particulars and to prepare himself for original experiment, let him search 

 out and peruse original papers, and let him consult the vegetable department of the several 

 elementary publications referred to, especially that of Dr. Thomson's System of Chemistry ; 

 the most distinguished and elaborate of all our elementary works on the subject, and the 

 guide chiefly applied to in the drawing up of the sketch that is here exhibited. 



CHAP. VIII. 

 Functions of Vegetables. 



715. From the analysis of the structure and principles of plants, the transition to their 

 life, growth, and propagation is natural and easy. This subject necessarily involves the 

 several following topics : germination ; nutriment ; digestion ; growth and developement 

 of parts ; anomalies of vegetable developement ; sexuality of vegetables ; impregnation of 

 the vegetable germen ; changes consequent upon impregnation ; propagation and disper- 

 sion of the species ; causes limiting the dispersion of the species ; evidence and cha- 

 racter of vegetable vitality. 



