132 OF THE LICHENS. 



CHAPTER XIII. 



OF THE LICHENS. 



Judging from external appearances and from their natural 

 habits, no two groups of plants would seern 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 ' 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 (Abro thallus 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 

 Algae. Agardh considers Lichens more nearly allied to 

 Fungals than to Algals : he remarks, that ' if Sphserias, or 

 Pezizas, had a thallus, they would be Lichens ; and that the 

 same part is all that determines such genera as Calycium, 

 Verrucaria, or Opegrapha to be Lichens and not Fungi.' 

 (Lindley, ' Vegetable Kingdom,' 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 c 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 



