X 
PREFACE. 
But really all considerations of difficulty ought to be put aside when 
it is remembered how much more satisfactory are the results to which 
we are brought by the study of Nature philosophically, than those 
which can possibly be drawn from the most ingenious empirical mode 
of investigation. This will be sufficiently apparent from a brief expla- 
nation of the distinctions of the classes into which the vegetable king- 
dom is divided in the following pages. 
One of the first things that strikes an enquirer into the structure of 
plants, is the singular fact, that while all species are capable of propa- 
gating their race, the mode in which this important function is accom- 
plished is essentially different in different cases. The great mass of 
plants produces flowers which are succeeded by fruits, containing seed, 
which is shed or scattered abroad, and grows into new individuals. But 
in Ferns, Mosses, Mushrooms, and the like, neither flowers nor seeds 
properly so called, can be detected, but propagation is effected by the 
dispersion of grains or spores which are usually generated in the sub- 
stance of the plant, and which seem to have little analogy with true 
seeds. Hence the vegetable world separates into two distinct groups, the 
FLOWERING and the FLOWERLESS. Upon examining more 
closely into the respective peculiarities of these two groups, it is found 
that flowering plants have sexes, while flowerless plants have none ; 
hence the former are are also called SEXUAL, and the latter ASEX- 
UAL. Then again the former usually possess a highly developed system 
of spiral or other vessels, while the latter are either altogether destitute 
of them, or have them only in the highest orders, and then in a peculiar 
state ; for this reason flowering plants are also VASCULAR, and flow- 
erless plants CELL ULAR, More than this, all flowering plants, when 
they form stems, increase by an extension of their ends, and a distension 
or enlargement of their sides ; but flowerless plants appear to form their 
stems simply by the addition of new matter to their points ; for this 
reason while the former are principally EXOGENS or ENDOGENS, 
the latter are called ACROGENS. Flowering plants also are for the 
most part furnished with respiratory organs or stomates, while flowerless 
plants are to a great extent destitute of them. No one then can doubt 
that in the vegetable kingdom two most essentially distinct divisions 
exist, the FLOWERING and the FLOWERLESS, and that these 
differ not in one circumstance only, but are most essentially unlike in 
a number of points both of organization and physiology. 
In like manner, FLOWERING PLANTS are themselves divisible 
