130 PRINCIPLES OF BOTANY, ETC. 
ever, have been sufficient to enable botanists to ar- 
range plants by their external characters, and this 
arrangement has been called a Natural System, 
(Systema naturale). 
Other botanists have founded their systems on 
the number, proportion and agreement of minute 
and not very obvious parts, and such a system has 
been called artificial, (systema artificiale). 
Others again select the sexual parts as the distince- 
tive characters, and found their system on the num- 
ber and variety of these parts. his is called the 
Sexual System, (systema sexuale). 
Sli 
Some of those natural families of plants, which 
the beginner ought to be well acquainted with, are 
the following : 
1. The rune; these are distinguished from 
other plants by their peculiar form, which is com- 
monly fleshy, coriaceous, or woody, fig. 4, 6, 7, 223, 
294, 225, | 
2. The ALGAE come somewhat near in their ap- 
pearance to other plants; but neither stem nor 
leaves are to be found in them. ‘Their form is very 
various; sometimes they have the appearance of 
flour or fibres; or they resemble the fret-work in 
architecture, fig. 3, 226. 
38. The musci, Mosses. In these the external 
appearance is almost the same with that of other 
plants, but their fruit and leaves are different. 
They are divided into, 
a. Musci frondosi: these have a capsule which 
1s 
