116 THE NATURAL SYSTEM. . 
Class VI. THALLOGENS, consisting merely of cellular tissue, with a tendency to 
grow into a flat expansion called thallus, but having no distinction of 
root, stem, leaves, or flowers. Ex. Lichens, seaweeds, liverworts, 
fungi. 
352. Affinities of the Six Classes. 'These may be represented 
to the sight by the following ai angement* 
Angiosperms. 
Gymnosperms. Aglumacee. 
Acrogens. Glumacee. 
Thallogens. 
Angiosperms stand in the highest rank, as they justly merit, by their superior 
organization. These are nearly allied to Gymnosperms by their mode of growth ; 
and, on the other hand, to Aglumacee by their mode of flowering. Gymnos- 
perms are intimately connected with Acrogens through Equisetacez of the latter, 
which stands intermediate; and the Aglumacez approach the Glumacez, almost 
indefinitely, through the Juncez (rushes). Between the Acrogens and Thallo- 
gens a close relationship is established through the Musci (mosses), while the 
sporogens form the connecting link between the Endogens and the lowest tribes 
of vegetation, as the Fungi. Thus, from the highest rank we descend to the low- 
est, through Gymnosperms and Acrogens on the one hand, and through Aglu- 
macez and Glumacez on the other, forming a circle of affinities. 
353. The mutual relations of the six classes with the higher divisions, are pre- 
sented in the following synopsis: 
| . § Class I. AnGIosPERMs. 
PHENOGAMIA; RET | Glass Il. GyMNOSPERMS. 
V. "IE _§ Class II. AcLtumacerous. 
Siar og NDOGENS}) Class IV. GLUMACEOUS. 
CRYPTOGAMIA | «eeceseccee Class V. AcCROGENS. 
: Class VI. THALLOGENS. 
354. Sus-citasses. The classes are next to be broken up 
into smaller divisions. In effecting this object most writers 
have employed artificial methods, since no natural one, founded 
upon clear and comprehensive distinctions, has yet been de- 
vised. Thus Angiosperms, which class is by far the largest of 
the six, is divided into three suwb-classes. PoLyPETAL&, or POLY- 
PETALOUS Exocens, flowers with distinct petals; MonoPErar2z, 
or MONOPETALOUS Exocens, flowers with united petals; Aprt- 
ALE, OF APETALOUS Exocens, flower with no floral envelopes, or 
with a calyx only. 
355. Orpers, or Famiuizs, are the most important of all the 
natural associations. On the accuracy and distinctness of the 
