2 A TEXTBOOK OF GENERAL BOTANY 
such as many kinds of medicine, perfumes, paper, ete. In 
breathing, animals take in oxygen. This is combined with car- 
bon, forming carbon dioxide, which is exhaled. All of the 
available oxygen would soon be exhausted and all animals ex- 
terminated if it were not for the fact that plants take in carbon 
dioxide, utilize the carbon, and liberate the oxygen. 
Even the remains of plants that have long been dead are 
useful to man. Among these are coal, which is used for fuel 
and which also yields gas, coke, and coal tar. The last named 
is the basis of the synthetic-dye industry and the source of 
many valuable medicines and other useful products. 
As human life is so intimately connected with and dependent 
upon plants, it is only natural that botany should be a subject 
of great interest; and it would seem that all educated persons 
should have some knowledge of it, if only for the purpose of 
understanding better so important a part of their environment 
as the vegetable kingdom. Such knowledge can hardly fail to — 
give one a keener appreciation and enjoyment of nature. 
While botany has great cultural value, the science is even 
more important on account of its useful applications. The 
applied branches, which are sometimes known as economic 
botany, are the most practical parts of the subject, but the 
theoretical branches also are useful. Although some of the 
applied branches, such as agriculture, horticulture, and forestry, 
have long since been separated from the parent science, their 
scientific application is dependent upon a knowledge of the 
fundamental principles of botany, and these applied branches 
have been continually improved by the employment of new 
principles discovered in the more theoretical fields. A knowledge 
of botany is useful not only to those engaged in the applied 
branches but also to everyone in daily life. It teaches us the 
values of different kinds of food and enables us to understand 
and control such processes as the spoiling of food, the decay of 
wood, the contamination of water supplies, and the molding of 
leather. Many uses will be evident as the student acquires 
familiarity with the subject. 
