112 THE NATURAL SYSTEM. 



Class Yl. TiiALLOGENS, consisting merely of cellular tissue, with a tendency to 

 grow into a fiat expansion called thallus, but having no distinction of 

 root, stem, leaves, or tiowcrs. Ex. Lichens, seawcedii, liverworts, 

 fungi. 



332. Affinities of the Six Classes. These may be represented 

 to the sight by the following arrangement' 



Angiosperms. 



Gymnosperms. Aglumaccro. 



Acrogens. GlumacccC. 



Thallogens. 



Angiosperms stand in the highest rank, as tliey justly merit, by their superior 

 organization. These are n(!arly allied to Gymnosperms by their mode of growth ; 

 and, on the other hand, to Aglumaccs by their mode of flowering. Gymnos- 

 perms are intimately connected with Acrogens through Equisetaceas of the latter, 

 which stands intermediate : and the Aglumaceai approach the Glumaccie, almost 

 indefinitely, through the Junccaj (rushes). Between the Acrogens and Thallo- 

 gens a close relationship is established through the Musci (mosses), while the 

 sporogms form the connecting link between the Endogens and the lowest tribes 

 of vegetation, as the Fungi. Thus, from the highest rank we descend to tlie low- 

 est, through Gymnosperms and Acrogens on the one hand, and through Aglu- 

 macea; and Glumacca; on the other, forming a circle of affinities. 



333. The mutual relations of the six classes with the higher divisions, arc pre- 

 sented in the following synopsis : 



I-p ( Class I. AxGiosrERJis. 



1.XOGENS; j f^iass II. Gymnosperms. 

 ( Class III. Aglumaceous. 

 E^°o«^^'^5J Class IV. Glu-maceous. 

 Kingdom ; , ^lass V. Acrogens. 



[ Cryptogamia ; ^ ^lass VI. Thallogens. 



334. Sub-classes. The classes are next to be broken up 

 into smaller divisions. In effecting this object most writers 

 have einployed artificial methods, since no natural one, founded 

 upon clear and comprehensive distinctions, has yet been de- 

 vi.sed. Tlius Angiosperms, which class is by far the largest of 

 ihc six, is divided into three sub-classes. Polyfetal^, or poly- 

 petalous Exogens, flowers with distinct petals; MonopetaljE, 

 or MONoPETALous ExoGENS, flowors with united petals; Apet- 

 AL.E, or APETALous ExoGENS, flower with no floral envelopes, or 

 with a calyx only. 



335. Orders, or Families, arc the most important of all the 

 natural associations. On the accuracy and distinctness of the 



