THE VOLATILE PART OF PLANTS. 53 
peculiar to itself, and usually the same plant in its different 
parts reveals to the senses of taste and smell the presence 
of several individual substances. In tea and coffee occurs 
an intensely bitter “ active principle,” thein. From tobacco 
an oily liquid of eminently narcotic and poisonous proper- 
ties, nicotin, can be extracted. In the orange are found 
no less than three o7/s ; one in the leaves, one in the flow- 
ers, and a third in the rind of the fruit. 
Notwithstanding the great number of bodies thus occur- 
ing in the vegetable kingdom, it is a few which form the 
bulk of all plants, and especially of those which have an agri- 
cultural importance as sources of food to man and animals. 
These substances, into whichany plant may be resolved by 
simple, mostly mechanical means, are conveniently termed 
proximate elements, and we shall notice them in some de- 
tail under six principal groups, viz: 
1, Water. 
2. The Crrtutose Grove or Amytoms—Cellulose, 
(Wood,) Starch, the Sugars and Gums. 
3. The Pecrosr Grovr—the Pulp and Jellies of Fruits 
and certain Roots. 
4, The VecrraBte Acrps, 
5. The Fars and Ors. 
6. The Atzumrvor or Prorerm Boptzs. 
1. Water, H, O, as already stated, is the most abundant 
ingredient of plants. It is itself a compound of oxygen and 
hydrogen, having the following centesimal composition : 
Oxygen, 88.88 
Hydrogen, 11.11 
100.00 
It exists in all parts of the plant, is the immediate cause 
of the succulence of the tender parts, and is essential to 
the life of the vegetable organs. 
In the following table are given the percentages of water in some of 
the more common agricultural products in the fresh state, but the pro- 
