o 



16 VEGETABLE ORGANOGRAPHY. 



presents the appearance of a foliaceous 'expansion, lying 

 on the ground, and shooting out roots or cramps ; thus, 

 following the forms of Jungermannia epiphylla, afterwards 

 of /. pinguis, we arrive by almost imperceptible trans- 

 itions to Anthoceros, Marchantia, and Riccia, in which 

 we perceive nothing more than a foliaceous disc, repre- 

 senting at the same time the stem and leaves, emitting 

 from one side roots and from the other the organs of 

 reproduction ; it is this foliaceous organ, which is neither 

 stem nor leaves, or at the same time both one and the 

 other, which has been named the Frons. 



Thus, the history of the Hepaticae tends to show, that 

 if for reasons of convenience and apparent analogy, 

 there have been described in these plants stems and leaves, 

 these organs are far from being distinct, as in vascular 

 plants, and that the mass of cellular ones, in appearance 

 the most compound, presents also a great homogeneity. 



Section IV. 



Of Lichens. 



The Lichens are still more remarkable than the 

 Hepaticae, by the union of these two circumstances, in 

 appearance contradictory — the prodigious variety of form 

 in different species, and the homogeneity of the tissue 

 of each. Among Lichens, some present plane expan- 

 sions, green, of a foliaceous appearance, and very analo- 

 gous to the structure of Riccia and Anthoceros: as 

 Loharia, &;c. Others have their whole substance 

 gelatinous, and thus approach the Algae and Tremeilae. 

 There are others, and a great number, which have the 



