22 



POPULAR HISTORY OF LICHENS. 



to under various names in the works of Dioscorides, Theo- 

 phrastus, and Pliny; but they do not appear to have at- 

 tracted much scientific attention, or to have become the 

 subjects of special classification till about the beginning of 

 the seventeenth century. The ideas of the earlier authors, 

 even for a considerable time subsequent to this period, re- 

 garding their nature and position in the scale of vegetation, 

 were of a very primitive and erroneous kind. Many species 

 were believed to be accidental or anomalous productions, 

 developed according to no known law, — growing under con- 

 ditions inimical to all other vegetation : hence the theory of 

 equivocal or spontaneous generation was advanced in ex- 

 planation of their origin and growth. One phasis of this 

 theory appeared in the doctrine that, according to the ex- 

 ternal circumstances by which they are surrounded in ger- 

 mination or genesis, — according as the medium in which 

 they arise and vegetate is earth, water, or decaying organic 

 matter, — certain vegetable cellules become Lichens, Algae, 

 or Fungi ; nay, some authors have even gone the length of 

 asserting, that under certain circumstances they are trans- 

 mutable into animalcules ! Another phase assumed the 

 form of a belief that the decomposition of organic bodies 

 gives origin to organic bodies lower in the scale of being, 



