THE CLASSIFICATION OF PLANTS, 79 
plants, which were formerly but little observed, have in con- 
sequence of the careful investigations of recent times been 
proved to present such a great variety of forms, and such a 
marked difference in their coarser and finer structure, that 
we must distinguish no less than fourteen different classes 
of them; whereas the number of classes of flowering plants, 
or Phanerogamia, may be limited to four. However, these 
erghteen classes of the vegetable kingdom can again be 
naturally grouped in such a manner that we are able to dis- 
tinguish in all sia main divisions or branches of the vege- 
table kingdom. Two of these six branches belong to the 
flowering, and four to the flowerless plants. The table on 
page 82 shows how the eighteen classes are distributed 
among the six branches, and how these again fall under the 
sub-kingdoms of the vegetable kingdom. 
The one sub-kingdom of the Cryptogamia may now be 
naturally divided into two divisions, or sub-kingdoms, differ- 
ing very essentially in their internal structure and in their 
externalform, namely, the Thallus plants and the Prothallus 
plants. The group of Yhallus plants comprises the two 
large branches of Tangles, or Algze, which live in water, and 
the Thread-plants, or Inophytes (Lichens and Fungi), which 
grow on land, upon stones, bark of trees, upon decaying 
bodies, ete. The group of Prothallus plants, on the other 
hand, comprises the two branches of Mosses and Ferns, 
containing a great variety of forms. 
All Thallus plants, or Thallophytes, can be directly recog- 
nized from the fact that the two morphological fundamental 
organs of all other plants, stem and leaves, cannot be dis- 
tinguished in their structure. The complete body of all 
Algze and of all Thread-plants is a mass composed of simple 
