xxiv INTRODUCTION 



In the absence of any "visible" seed, there was much speculation in 

 early days as to the genesis of all the lower plants and many opinions 

 were hazarded as to their origin. Luyken 1 , for instance, thought that lichens 

 were compounded of air and moisture. Hornschuch 2 traced their origin to 

 a vegetable infusorium, Monas Lens, which became transformed to green 

 matter and was further developed by the continued action of light and air, 

 not only to lichens, but to algae and mosses, the type of plant finally evolved 

 being determined by the varying atmospheric influences along with the 

 chemical nature of the substratum. An account 8 is published of Nees von 

 Esenbeck, on a botanical excursion, pointing out to his students the green 

 substance, Lepraria botryoides, which covered the lower reaches of walls and 

 rocks, while higher up it assumed the grey lichen hue. This afforded him 

 sufficient proof that the green matter in that dry situation changed to 

 lichens, just as in water it changed to algae. An adverse criticism by 

 Dillenius 4 on a description of a lichen fructification is not inappropriate to 

 those early theorists : " Ex quo apparet, quantum videre possint homines, 

 si imaginatione polleant." 



A constant subject of speculation and of controversy was the origin of 

 the green cells, so dissimilar to the general texture of the thallus. It was 

 thought finally to have been established beyond dispute that they were 

 formed directly from the colourless hyphae and, as a corollary, Protococcus 

 and other algal cells living in the open were considered to be escaped 

 gonidia or, as Wallroth 8 termed them, " unfortunate brood-cells," his view 

 being that they were the reproductive organs of the lichen plant that had 

 failed to develop. 



It was a step forward in the right direction when lichens were regarded 

 as transformed algae, among others by Agardh 6 , who believed that he had 

 followed the change from Nostoc lichenoides to the lichen Collema limosum. 

 Thenceforward their double resemblance, on the one hand to algae, on the 

 other to fungi, was acknowledged, and influenced strongly the trend of study 

 and investigation. 



The announcement 7 by Schwendener* of the dual hypothesis solved the 

 problem for most students, though the relation between the two symbionts 

 is still a subject of controversy. The explanation given by Schwendener, 

 and still held by some 9 , that lichens were merely fungi parasitic on algae, 

 was indeed a very inadequate conception of the lichen plant, and it was hotly 

 contested by various lichenologists. Lauder Lindsay 10 dismissed the theory 

 as " merely the most recent instance of German transcendentalism applied 



1 Luyken 1809. 2 Hornschuch 1819. 8 Raab 1819. 4 Dillenius 1741, p. 200. 



4 Wallroth 1825. 8 Agardh 1820. " See p. 27. 8 Schwendener 1867. 



9 Fink 1913. 10 Lindsay 1876. 



