48 OUTLINE OF STRUCTURAL BOTANY 
plants certain characters must be chosen which are common to one 
group and which are absent from another. 
Thus we may commence with the individuals which are most 
alike and proceed toward those which have the least number of 
common characteristics or we may commence with those having 
but few characters in common and proceed to those in which most 
of the characters are common. 
The system which we may adopt may be an artificial one, such, 
for example, as the tlistinction between trees and herbs, water 
plants and land plants and other such characters. The beautiful 
system of Linnaeus which served so long as an almost indispensable 
aid in the study of plants was an artificial one based, for flowering 
plants, in great part, upon the number and relations of the stamens 
and pistils. Even now this system is perhaps the most convenient 
for the determination of the species. 
It has, however, in later times, given way to the system known 
as the natural method which has infinitely greater scientific value. 
It is in fact based, so far as our knowledge extends, upon the theory 
of genealogical descent, determined by the analogy of characters. 
To this we have referred in the preceding section. 
It would be impracticable in this place to indicate every element 
in such a great system, but for our present purpose we may con- 
sider the first great division in the plant kingdom as that which 
places all plants propagated by seeds in one class and those which 
are perpetuated without seeds in another. 
The plants included in this work belong to a single Grand Divi- 
sion of the Vegetable Kingdom. They are Hmbryo-bearing Plants 
(technically) Hmbryophyta. 
This Grand Division is also called the Division of Flower-Bearing 
Plants. It is characterized by the fact that the succeeding gener- 
ations are developed from true seeds which contain in themselves 
an embryo stem which terminates at one extremity in what is known 
as the plumule, the embryonic first leaf or leaves, and at the other 
extremity as the radicle or embryonic rootlet. 
The seed containing the embryo is always developed while con- 
nected with the parent plant. 
Ferns, true mosses, mushrooms and other non-flowering plants 
are propagated by a different form of generation. ‘The non-flower- 
ing species of higher development are propagated by spores which 
differ from seeds in being less specialized and apparently less 
elevated in the scale of development. In the lowest orders propa- 
gation is by simple division of the cell constituting the plant or by 
the formation within the parent cell of a group of similar cells 
