20 POPULAR FIELD BOTANY. 
NATURAL SYSTEM.* 
Plants in the Natural system of De Candolle are divided 
into three great classes, Hxogens, Hndogens, and Acrogens. 
I. EXOGENS. 
Ezxogens include all those plants the stem of which contains 
pith, and the additions to the size formed on the outside 
of the last layer: hence the name evogens. The veins of 
the leaves are branched, forming net-work, and the seed 
produces two primary leaves ; the class is, therefore, also 
called Dycotyledonous. It embraces most of our plants: 
Lilies, Grasses, Orchises, &c. excepted. 
This class is divided into four sub-classes, Thalamiflore, 
Calyciflore, Corolliflora, Monochlamydee. 
lst SuB-cLAss. 
TuHaLaMIrLorz.—Flowers usually furnished with both calyx 
and corolla, the latter consisting of distinct petals, or 
* If the reader wishes to study the Natural System of classification, the 
same care and attention are necessary as in the Artificial, and greater 
nspection and expenditure of time; for the parts to be examined are more 
minute in many cases, and require a good maguifying glass to help the 
sight. 
