DEPARTMENTS OF BOTANY 9 
edge of the structure of plants, just as an account of the 
different kinds of steam-engines (e. g., locomotives, including 
freight-engines, passenger-engines, switching-engines, etc.; 
stationary engines, including horizontal engines, pumping- 
engines, hoisting-engines, and so on) would be a description 
of the form and position of the different parts of their ma- 
chinery. Moreover, not until we know about the different 
parts of a plant, as of a machine, are we in position to under- 
stand well what each part is for, and how they all work to- 
gether. A knowledge of plant structure has thus a twofold 
importance. Similarly a knowledge of the materials which 
enter into the various parts of a plant, as of a machine, is 
necessary if we would understand its capabilities and use- 
fulness. 
So one question leads to another, the proper appreciation 
of one aspect of plants requiring also the study of other 
aspects. In this way have arisen the different departments 
of botany, each one representing a special point of view and 
all being necessary to a comprehensive understanding of the 
subject. 
To the various departments have been given special names 
of which the following are the most important for a beginner 
to remember :-— 
Economic Botany views plants in their relation to man’s 
welfare. It is concerned with all the kinds which man uses 
for food, medicine, clothing, shelter, ornament, or for other 
purposes; and all which are harmful to him as weeds, poisons, 
or pests. The ways in which these plants are useful or harm- 
ful, and to what extent, to what peoples, for how long, and 
why—such questions as these it seeks to answer as far as 
possible. 
Chemical Botany is the study of the properties and quanti- 
ties of the various substances found in plants. Since the 
value of a useful plant often depends upon the presence of 
some special substance, such as sugar, the economic botanist 
has frequent occasion to learn about the chemistry of the 
plants with which he deals. Such knowledge is also necessary 
to an understanding of the life-processes of plants. 
Systematic Botany is concerned with the accurate descrip- 
