i8 HISTORY OF LICHENOLOGY 



H. Period VII. 1867 and after 



Modern lichenology begins with the enunciation of Schwendener's' theory 

 of the composite nature of the lichen plant. The puzzling resemblance of 

 certain forms to algae, of others to fungi, had excited the interest of botanists 

 from a very early date, and the similarity between the green cells in the 

 thallus, and certain lower forms of algae had been again and again pointed 

 out. Increasing observation concerning the life-histories of these alga^ and 

 of the gonidia had eventually piled up so great a number of proofs of their 

 identity that Schwendener's announcement must have seemed to many an 

 inevitable conclusion, though no one before had hazarded the astounding 

 statement that two organisms of independent origin were combined in the 

 lichen. 



The dual hypothesis, as it was termed, was not however universally 

 accepted. It was indeed bitterly and scornfully rejected by some of the 

 most prominent lichenologists of the time, including Nylander^ J. Miiller 

 and Crombie^ Schwendener held that the lichen was a fungus parasitic 

 on an alga, and his opponents judged, indeed quite rightly, that such a view 

 was wholly inadequate to explain the biology of lichens. It was not till a 

 later date that the truer conception of the "consortium" or "symbiosis" was 

 proposed. The researches undertaken to prove or disprove the new theories 

 come under review in Chapter II. 



Stahl's work on the development of the carpogonium in lichens gave a 

 new direction to study, and notable work has been done during the last forty 

 years in that as in other branches of lichenology. 



Exploration of old and new fields furnished the lichen-flora of the world 

 with many new plants which have been described by various systematists — 

 by Nylander, Babington, Arnold, Miiller, Th. Fries, Stizenberger, Leighton, 

 Crombie and many others, and their contributions are scattered through 

 contemporary scientific journals. The number of recorded species is now 

 somewhere about 40,000, though, in all probability, many of these will be 

 found to be growth forms. Still, at the lowest computation, the number of 

 different species is very large. 



Systematic literature has been enriched by a series of important mono- 

 gra,phs, too numerous to mention here. While treating definite groups, they 

 have helped to elucidate some of the peculiar biological problems of the 

 symbiotic growth. 



Morphology, since Schwendener's time, has been well represented by 

 Zukal, Reinke, Lindau, Fiinfstijck, Darbishire, Hue, and by an increasing 

 number of modern writers whose work is duly acknowledged under each 



' Schwendener 1867. ^ Nylaniler 1874. '■> Crombie 1881;. 



