BET. J. M. CBOMBIE ON THE ALGO-LICHEN HYPOTHESIS. 281 



which many of them present, especially when sterile. If, then, 

 the gonimia originate, as they certainly do, in these cellules, they 

 necessarily belong to the licben-thallus, of which, as we have 

 already seen, they are special and important organs. Conse- 

 quently they cannot be algals, as Schwendenerism erroneously 

 assumes. Moreover, as the species of which the Ephebacei are 

 composed possess no lichenohyphae whatever, the theory is in 

 their case evidently impossible. 



From all these various considerations and illustrations, to which 

 others, though of minor importance, might easily be added, it is 

 clear that the Algo-lichen hypothesis rests upon no solid basis 

 whatever, but simply aud solely upon imagination, and that it is 

 merely a plausible attempt to explain certain phenomena which 

 its author and adherents supposed to be otherwise inexplicable. 

 Notwithstanding the laboured arguments by which it has been 

 sought to deprive them of their autonomy and intrude them 

 amongst the Ascomycetes, Lichens still remain a distinct class of 

 plants, intermediate between the Alga? and the Fungi, related to 

 the former through the Ephebacei and to the latter through 

 various species of their lower genera. It is no doubt difficult at 

 times to draw a definite line of demarcation between some of 

 them and these other two classes ; but this is only what often 

 happens elsewhere, till more accurate observation at length solves 

 the difficulty *. At the same time, however, with respect to 

 Lichens, all correct observations and logical deductions show 

 that the words of Acharius in the conclusion of the Intro- 

 duction to his ' Lichenographia Universalis ' (p. xiv) are still 



as true as when he wrote them : — " Uti ratum habeo : 



Lichenes ordinem naturalem peculiarem et a reliquis plantis 

 Cryptogamis distiuctum constituere." Distinct they certainly 

 are alike in the structure of their thallus and the mode of their 

 nutrition, and more peculiar still in their very slow and inter- 



* Indeed, as every systematist well knows, it is constantly becoming more 

 and more difficult to draw any such definite lines, especially in several of the 

 lower Orders of plants. Living nature in its wild luxuriance (whether as the 

 result of evolution or degradation of primordial types) refuses to be bound by 

 strictly mathematical laws. Hence the limits of Classes (or Orders, &c.) must 

 to a certain extent necessarily vary as our biological researches are more ex- 

 tended and minute. In enabling us in many cases to ascertain such limits with 

 any precision, chemistry will no doubt play a still more important part in the 

 near future than it has hitherto done. 



