678 
THE PRINCIPLES OF BOTANY. 
We have already pointed to the classes into which flowering 
plants have been divided, it will, therefore, be well in the 
present article to direct attention to some of the more 
important plants in the different divisions. Leaving out, 
therefore, Class III, Rhizogens, as not containing any 
economic species, we proceed to notice Class IV, Endogens. 
In endogens, as the name implies, we have plants whose 
woody stems have their newest parts in the centre, as dis- 
tinguished from exogens, whose newest wood forms a concen- 
tric layer outside the previously-formed layers. 
The cotyledon is a single piece, e. g. a wheat grain, and not 
in two pieces as in the pea and bean. Hence, then, by some 
this class has been termed mono -cotyledonous = endogen, as 
contrasted with dicotyledonous = exogen. 
The leaves are parallel-veined and persistent, that is, are 
not liable to that phenomenon known as the fall of the leaf — 
separation of the leaf from the stem by a natural division ; 
hence, then, in exogens the leaf which is net-veined is 
deciduous. 
This class of endogens is a very large one, and one too 
largely distributed over the different quarters of the globe. 
Professor Lindley has classed it under eleven alliances, which 
we epitomise as under : 
Class IY, Endogens. 
# Flowers glumaceous (that is to say, composed of bracts not col- 
lected in true whorls, but consisting of imbricated colourless or herba- 
ceous scales). 
Glumales. 
## Elowers petaloid, or furnished with a true calyx or corolla, or 
with both, or absolutely naked ; male or female, or sexes in different 
flowers. 
Arales. 
Palmales. 
Hydrales. 
Elowers furnished with a true calyx and corolla adherent to the 
ovary; male and female flowers together. 
Narcissales. 
Anomales. 
Orchid ales. 
#### Elowers furnished with a true calyx and corolla, free from the 
ovary, male and female together, sometimes male or female, or 
separate. 
Xyridales. 
JUNCALES. 
Liliales. 
Alismales. 
