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OF THE LICHENS. 
CHAPTER XIII. 
OF THE LICHENS. 
Judging from external appearances and from their natural 
habits, no two groups of plants would seem to be more 
distinctly separated than the Fungi and the Lichens. Their 
boundaries, one would suppose, are as sharply defined as 
any embraced under the great family of Cryptogamia. 
Nevertheless, modern authors are gradually drawing to 
the opinion that, sooner or later, the Lichens must be 
reduced to mere forms of the Fungal class. The point on 
which the ‘ Separatists 7 have mainly relied is the presence, 
in the thallus, of globular gonidia, containing a green 
matter in the cells, which gonidia are supposed to be 
wanting in the Fungi ; but it is certain that some of the 
Lichens (Abrothallus for example) are destitute of green 
gonidial cells. And it is by no means certain that some 
analogous structure is not to be found in many of the 
Algse. Agardh considers Lichens more nearly allied to 
Fungals than to Algals : he remarks, that 1 if Sphasrias, or 
Pezizas, had a thallus, they would be Lichens ; and that the 
same part is all that determines such genera as Calycium, 
Verruca ria, or Opegrapha to be Lichens and not Fungi. 7 
(Lindley, ‘Vegetable Kingdom, 7 47.) 
However, 'eaving these matters to be discussed by 
physiologists, we will assume for our purposes, that the 
distinction ordinarily laid down in regard to the two 
classes is correct, viz. that ‘ while the Fungi have their 
vegetative structure immersed in the medium in which 
they grow, the Lichens are entirely aerial encrusting plants. 
A practical matter of great importance to the collector, 
though of no value in the eyes of the systematist, is the 
