110 HOW CROPS GROW. 



parts of plants usually contain chlorophyll only at their bdrface, 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 soluola 

 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 



Fremj has shown that chlorophyll may be easily decomposed into two 

 coloring matters, a yellow, Zaidhopliyll, and a blue, Cyanophyll. This ia 

 accomplished by treating chlorophyll with a mixture of chlorhydric add 

 and ether ; the cyanophyll dissolves in the latter, and the zanthophyl i is 

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

 perhaps due to zanthophyll. 



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

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

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

 into chlorophyll. 



Tannin 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 chemical composition. The tannins are weak 

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

 curid (from nut-galls), Caffeotannic acid (from coffee), Quei titannic acid 

 (from the oak), etc. As already hinted, the tannins are Glucovides, orfl 

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

 sugar is glucose, and the substance 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 formulae: 



Tannin. Water. Gallic acid. Glucose. 



2 (C 27 H 22 O 17 ) + 8 (H 2 O) = 6 (C, H. O 6 ) + C, a H 24 O 13 



THE ALKALOIDS are a class of bodies very numerous in poisonous and 

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

 Those which have an agricultural interest are Nicotin, Caffein, and 

 Theobromin. 



I\icoliii, C 10 H 14 N 2 , is the narcotic and extremely poisonous prin 

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



