6 
INTRODUCTION. 
A compromise between these aims must be effected, deter¬ 
mined largely by the necessities of the moment. Economic 
Botany, if it is to become a science, and its professors, if 
they are ever to become more than mere rule-of-thumb 
empirics, must attend to all classes of vegetable products, 
comparing together all the facts obtained, classifying them, 
and drawing conclusions from them, with the object of 
finding out general laws of wide applicability. At the same 
time, the chief attention must, as a rule, be devoted to the 
staple products of the vegetable kingdom, with the object 
of obtaining as much immediately valuable knowledge as 
possible. Only, however, by wide study of all classes of 
plants and their products can this knowledge ever be more 
than empirical. Gradually, by the study of vegetable products 
and the physiological processes involved in their production 
in the plant, we shall obtain a clearer insight into the 
principles that govern the production, and have it at last in 
our power intelligently to control this production to suit 
our own ends. 
Whilst, however, the student of Economic Botany must 
go into all the facts and deal with all classes of vegetable 
products, this is not what the general reader requires. 
What he wants is a succinct statement of the received 
principles of the subject, the general conclusions and laws 
at which its students have arrived, the essential detailed 
facts about the more important products of plants, and the 
outlines of the more important facts about the minor pro¬ 
ducts, sufficient to guide him from mistakes in dealing with 
them. It is from this point of view that the present work 
is written. 
The Sources off the Economic Products of the 
Vegetable Kingdom. 
Products of value are derived from an enormous number 
of different plants, and from a great number of different 
parts of plants. Roots, stems, leaves, bulbs, tubers, flowers, 
stamens, fruits, seeds, &c., are all possible sources of valuable 
