110 HOW CEOPS GUOW. 



parts of plants usually contain chlorophyll only at their surface, and 

 in quantity no greater than colored fabrics contain the particles of dye. 



Chlorophyll being soluble in ether, accompanies fat or wax when these 

 are removed from green vegetable matters by this solvent. It is soluble 

 in chlorhydric and sulphuric acids, imparting to these liquids its in- 

 tense green color. According to Pfaundler, the (impure?) chlorophyll 

 of grass has the following percentage composition : 

 Carbon 60.85 

 Hydrogen 6.39 

 Oxygen 32.78 



Fremy has shown that chlorophyll may be easily decomposed into two 

 coloring matters, a yellow, ZanUiophyll, and a blue, Oyanopliyll. This is 

 accomplished by treating chlorophyll with a mixture of chlorhydric acid 

 and ether ; the cyanophyll dissolves in the latter, and the zanthophyll is 

 taken up by the former solvent. The yellow color of autumn leaves is 

 perhaps due to zanthophj'll. 



According to Sachs, there exists in those parts of plants, which, though 

 not green, are capable of becoming so, a colorless substance, Zeitcopjiyll, 

 which, in contact with oxygen, acquires a green color, being converted 

 into chlorophyll. 



Xannin is the general designation of the bitter, astringent prin- 

 ciples, (used in leather-making,) of the bark and leaves of the hemlock, 

 oak, sumach, plum, pear, and many other trees, of tea, coffee, and of 

 gall-nuts. It is found in small quantity in the young bean plant, and in 

 many germinating seeds. 



Tannin is closely related to the carbohydrates, as is demonstrated 

 alike by the microscopic study of its development in the plant, and by 

 our knowledge of its cliemical composition. The tannins are weak 

 acids, and are distinguished, according to their origin, as Oallotannic 

 acid (from nut-galls), Caffeotannic acid (from coffee), Qiiei'citamiic acid 

 (from the oak), etc. As already hinted, the taunius are Glucosides, or 

 compounds of sugar, with some other substance. In gall-tannin the 

 sugar is glucose, .and the 'feubstauce associated with, or rather yielded by 

 it on decomposition, is known as Gallic acid. By boiling gall-tannin 

 with a dilute acid, or by subjecting its solution to fermentation, decom- 

 position into the two substances named is accomplished. 



According to Streckcr, the composition of gall-tannin and this con- 

 version are indicated by the following formula; : 



Tannin. ^Valcr. Gallic acid. Glucose. 



3 (C„ Hs2 0„) -I- 8 (H-, O) = 6 (Cr H„ O5) + Cjs Hj, On 



TuE Alkaloids are a class ol bodies very numerous in poisonous and 

 medicinal plants, of which they usually constitute the active principle. 

 Those which have an agricultural interest are S'icotin, Caffein, and 

 Thedbromin. 



Nicotin, Cio Hii N,, is the narcotic and extremely poisonous prin- 

 ciple in tobacco, where it exists in combiuatiou with malic and citric 



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