116 Tlii: .\AlURAL SYSTEM. 



Class VI. Thallogens, consisting merely of cellular tissue, -witli a tendency to 

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

 root, stem, leaves, or flowers. Ex. Lichens, seaweeds, livenvorts, 

 fungi. 



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

 to the sight by the following arrangement • 



Angiospeims. 



Gymnosperms. Aglumacefe. 



Acrogens. Glumacea;. 



Thallogens, 



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

 organization. These are nearly allied to Gpnnosperms by their mode of growth ; 

 and, on the other hand, to Aglumaeeae by their mode of flowering. GjTnnos- 

 pcrms are intimately connected with Acrogens through Equisetacetc of the latter, 

 which stands intermediate; and the AglumaccEe approach the Glumaceie, almost 

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

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

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

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

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

 macea; and Glumacese on the other, forming a circle of afiinities. 



353. The mutual relations of the six classes with the higher divisions, are pre- 

 sented in the following synopsis : 



{•p , ( Class I. ANGiosi'Enjis. 



1.X0GLX&; <Q II. Gymnosperms. 

 I Class III. Aglumaceous. 

 , ExDOGENS; j Class IV. Geumaceous. 



Ivingi>om;1 ( Class V. Acrogens. 



{ Crtptogamia ; j ^lass VI. Thallogens. 



354. SuB-CLASSEs. The classes are next to be broken up 

 into smaller divisions. In effecting this object most wniters 

 have employed artificial methods, since no natural one, founded 

 upon clear and comprehensive distinctions, has yet been de- 

 vised. Thus Angiosperms, Avhich class is by far the largest of 

 llic six, is divided into three sub-classes. PoLYPETAL.ai:, or poly- 

 TETALous ExoGENS, flowers with distinct petals; MoNorEXALiE, 

 or MONopETALous ExoGENs, flowors witlx united petals; Apet- 

 AL.'E, or APETALous ExoGENS, flow^er with no floral envelopes, or 

 with a calyx only. 



355. Orders, or Fajiilies, are the most important of all the 

 natural associations. On the accuracy and distinctness of the 



