VEGETABLE ACIDS. 121 



is the sleeping germ recalled to life, by the access of air and warmth 

 and duly tempered moisture, than a new agent is summoned to its aid, 

 and the food is so changed as to be rendered capable of ministering to its 

 early wants. The first movement of the nascent germ — (and how it 

 moves, by what inherent or impartial force, who shall discover to us ?) 

 — is the signal for the appearance of this agent — diastase — of which, 

 previous to germination, no trace could be discovered in the seed. At 

 the root of tlie germ, where the vessels terminate in the farinaceous 

 matter, exactly where it is wanted, this substance is to be found; — there, 

 and there only, resolving and transforming the otherwise unavailable 

 store of food, and preparing it for being conveyed either to the ascending 

 sprout or to the descending root. And when the necessity for its yjre- 

 sence ceases — when the green leaf becomes developed, and the root has 

 fairly entered the soil — when the plant is fitted to seek food for itself — 

 then this diastase disappears, it undergoes itself a ne\^ conversion, and is 

 prepared in another form to contribute to the further increase of the plant. 

 How beautiful and provident are all these arrangements ! — how plas- 

 tic the various forms of organic matter in the hands of the All-Intelli- 

 gent! — how nicely adjusted in time and place its diversified changes! 

 What an apparently lavish expenditure of forethought and kind previ- 

 sion, in behalf even of the meanest plant that grows ! 



§ 9. Vegetable Acids. — Acetic acid, Oxalic acid. Tartaric acid, 

 Citric acid, Malic acid. 

 Another class of compound substances remains to be shortly consid 

 ered, — those, namely, which possess sour or acid properties, and which 

 are known to be present in large quantity in many plants, and more 

 especially in the greater number of unripe fruits. They do not, taken 

 as a whole, form any large portion of the entire produce, either of the 

 general vegetation of the globe or of those plants which are cultivated 

 for food ; yet the growth of fruit — as in the grape, orange, and apple 

 countries — is sufficiently extensive, and the general interest in the cul- 

 tivation of fruit trees sufficiently great, to require that the nature of the 

 substances contained in fruits, and the peculiar changes by which they 

 are formed, should be in some measure considered and explained. 



I. ACETIC ACID. 



Acetic acid or vinegar is the most extensively diffijsed, and the most 

 largely produced, of all the organic acids. It is formed during the ger- 

 mination of seeds, and it exists in the juices of many plants, but it is 

 most abundantly evolved during the fermentation, whether namral or 

 artificial, of nearly all vegetable substances. When pure it is a colour- 

 less liquid, having a well known agreeably acid taste. ^ It may be 

 boiled and distilled over without being decomposed. The vinegar of the 

 shops is generally very much diluted, but it can be prepared of such a 

 strength as to freeze and become solid at 45° F., and to blister the skin 

 and produce a sore when applied to any part of the body. When 

 mixed with water it readily dissolves lime, magnesia, alumina, &c., 

 forming salts called acetates, which are all soluble in water, and may, 

 therefore, be readily washed out of the soil or of compost heaps by 

 heavy falls of rain. 



