110 HOW CROPS GROW. 
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, Zanthophyll, and a blue, Cyanophyll. 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 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 Gallotannie 
acid (from nut-galls), Caffeotannic acid (from coffee), Quercitannie acid 
(from the oak), etc. As already hinted, the tannins are @Glucosides, or 
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 ucid, or by subjecting its solution to fermentation, decom- 
position into the two substances named is accomplished. 
According to Strecker, the composition of gall-tannin and this con- 
version are indicated by the following formule: 
Tannin, Water. Gallic acid. Glucose. 
2 (Coy Hos Orr) + 8 (Ha O) = 6 (Cz Hy Os) + Cia Hoa Orn 
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 Wicotin, Caffein, and 
Theobromin. 
Nicotin, Ci, H,, No, is the narcotic and extremely poisonous prin- 
ciple in tobacco, where it exists in combination with malic and citric, 
