46 



POPULAR, HISTORY OF LICHENS. 



In the progress of onward development there is first no- 

 ticed, superimposed upon the filamentous network of the 

 hypothallus, a layer of spherical or rounded cellules, colour- 

 less or whitish, in close union both with each other and with 

 the subjacent filaments. Upon this cellular stratum there 

 is gradually deposited a second, w T hich is characterized by its 

 constituent cellules being quite globular, free in relation to 

 each other and subjacent textures, and more or less full 

 of chlorophyll granules; these cellules are the gonidia of 

 which we have already spoken. We have now attained the 

 essentials of the Lichen- th alius, viz. gonidia, or isolated cel- 

 lules, and filaments, with which they are intermixed. In some 

 species the thallus attains no higher development, as in the 

 Verrucarite, the most simply organized Lichens. Such Lichens 

 appear indeed destitute of a thallus, but careful microscopic 

 examination will detect the elements we have described. 

 These elements, or, in other words, the possession of this 

 simple and rudimentary thallus, are the only means of dis- 

 tinguishing many Augiocarpous Lichens from species of 

 Sphteria, belonging to the allied great family of Fungi. In 

 the common Verrucarice and Graphidece of our tree-barks the 

 fructification however appears to spring directly from the sur- 

 face of the bark, and may in a certain sense be said to con- 



