BET. J. M. CKOMBIE ON THE ALGO-LICHEN HYPOTHESIS. 259. 



On the Algo-Lichen Hypothesis. 



By the Eev. James M. CboA^bie, F.L.S. 



[Eead 12th April, 1884.] 



(Plates VIII. & IX.) 



I need scarcely say that one of the most interesting biological 

 problems of the day, in so far at least as relates to Vegetable 

 Morphology and Physiology, is connected with the theory usually 

 known under this appellation, or, as it might more correctly be 

 called, the Algo-Fun gal-Lichen hypothesis. This is sufficiently 

 proved by the now yery extensive literature of the subject and 

 by the various discussions to which it has given rise. To give 

 any detailed resume of that literature, or to enter minutely into 

 these discussions, is as foreign to my present purpose as it is 

 unnecessary for the elucidation of the subject. It will suffice 

 that I bring under your notice, as succinctly as is consistent 

 with a due understanding of the question, the presumed grounds 

 on which the hypothesis rests and the ascertained facts by which 

 it is subverted. 



Now the problem to be solved is — What is the origin of the 

 Hchen-gonidia, and in what relation do they stand to the thallus ? 

 In premicroscopical days, as might be expected from the nature 

 of the case, nothing on these points was either known or written. 

 Indeed, by the earlier Hellenists the gonidia were scarcely, if at 

 all, distinguished ; and it was not until 1825 that they were first 

 distinctly recognized by Wallroth (' Naturgeschichte der Flech- 

 ten'), who supposed that they were the asexual reproductive 

 organs of Lichens, and so gave them their distinctive appella- 

 tion. Even in Koerber's Dissertation " De Gonidiis Lichenum " 

 (1839), in which they are treated more fully and accurately 

 than in any previous work, nothing is adduced as to their genesis 

 or their relation (except in the case of soredia) to the other 

 elements of the thallus. The first who gave any explanation 

 of the matter was Bayrhoffer, who, in 1851 ('Einiges iiber die 

 Lichenen und deren Befruchtung') stated that " the threads of 

 the fibrous stratum " swell at the top, which swellings after- 

 wards become "male gonidia." This was subsequently con- 

 firmed by Speerschneider (Bot. Zeit. 1853 Ac), and supported 

 (with a slight modification) by Schweudener (in JSageli, Bei- 

 trage zur Wissen. Bot. ii. 1859, p. 125, t. i. fig. 18, t. v. fig. 6), 



1IJTX. JO^KN. — EOTANT, VOL. XXI. u 



