Bey Special M orphology and Classification. 239 
- still further intermediate grades; thus a Subfamily isa 
grade between family and tribe, a Swd-dribe a grade between 
tribe and genus, &c. | 
Classifications of plants which are carried out according to definite 
principles are called systems, and are distinguished as Natural — 
Artificial systems. 
Natural Systems are constructed synthetically ; z.¢. they ascend 
from the individual upwards, placing always in juxtaposition those 
forms which are most nearly related, and thus, by the continual group- 
ing of the most nearly related forms in each stage, attaining a gradual 
and general view of the entire vegetable kingdom. A natural system 
may therefore be called a Grammar of the Vegetable Kingdom, since it 
explains all the laws and relationships according to which distinct in- 
dividuals are united into species, genera, families, orders, classes, &c., 
in short, into one harmonious whole. Much is, nevertheless, left to 
the arbitrary decision of each naturalist ; although a moderate degree 
of unanimity has now been arrived at with respect to the boundaries of 
the different orders. The orders are therefore the unities out of which 
the vegetable kingdom is constructed, although they have not yet 
been grouped into a perfect natural system. The natural system has 
been compared, but not very happily, to a chain, a copiously branched 
tree, oranet. The best simile is that of Linnzus, who compared the — 
various reciprocally related families to the countries of a continent, to 
which peninsulas are attached by slight connections, and near which are 
islands representing isolated families. 
Artificial systems are, on the contrary, constructed analytically, and 
set out in the opposite direction, the whole ground being broken up by 
repeated divisions, in accordance with a predetermined principle of | 
classification, until finally you arrive at the individual plant. They 
may be compared to dictionaries, in which the whole vocabulary is 
arranged according to the one principle of an alphabetical arrange- 
ment, artificial systems being in the same manner characterised by the. 
arrangement of the total number.of genera in accordance with a single 
principle. Both place together things that differ most widely ; but 
both enable any desired word or any particular plant to be easily 
found, or to have its place assigned it among the rest. Strictly speak- 
ing, an artificial system ought to be based on only a single principle 
of classification, or rather on the more or less perfect development of 
a single organ; but usually the characters of several are taken into 
account. It would be possible for there to be many artificial systems 
of equal value ; and as long ago as 1765, Adamson enumerated 65. 
