260 EEV. J. M. CEOMBIE ON THE ALGO-LICHEN HTPOTnESIS. 



as also by De Bary (' Morphologie und Physiologie der Pilze 

 Flechten,' &c, 18G5). According to this theory the gonidia 

 originate from the hyphsD in the manner succinctly described by 

 Th. M. Fries, in Scand. (p. 7), who embraces and defends it as 

 the result of his own observations. " The hyphse," he says, " are 

 not only elongated into filaments, but they also put forth short 

 branchlets. The terminal cell of such branclilet is gradually 

 dilated, becomes subglobose, and is at length filled with chloro- 

 phyll (or a subsimilar coloured matter) ; in a few that cellule is 

 changed into a gonidium, and then, variously divided, originates 

 other gonidia." 



This view of the genesis of the gonidia from the hyphse, which 

 Avas quite erroneous, was for some time generally accepted with- 

 out further inquiry ; although, as we shall afterwards see, there 

 were certain other and different observations made previously to 

 those of Speerschneider, which were either entirely overlooked 

 or not rightly understood. In 1868, however, Prof. Schwen- 

 dener, reviewing the original notion on this subject, towards the 

 end of a paper entitled " Untersuchungen fiber den Flechten- 

 thallus," and more especially in a subsequent treatise, ' Die 

 Algen-typen der Plechten Gronidia ' (I860), rightly affirms that 

 the actual development of a gonidium from the terminal cell of a 

 hypha had not with certainty been observed, but only assumed 

 by authors. Accordingly he enunciated an entirely new theory 

 on the subject, which was evidently based upon a suggestion 

 previously made by De Bary. This latter celebrated crypto- 

 gamist, in his paper already referred to (p. 291), observing the 

 resemblance between the gonidia of some Collemacei and certain 

 of the lower Algse, came to the following conclusion : — " Either 

 the Lichens in question," he says, " are the perfectly developed 

 states of plants whose imperfectly developed forms have hitherto 

 stood amongst Algas as Nostocaceae and Chroococcacere, or the 

 Nostocacea? and the Chroococcacese are typical Algae which assume 

 the form of Collema, Ejphebe, &c, through certain parasitic Asco- 

 mycetes penetrating into them, spreading their nvycelia into the 

 continuously growing thallus, and frequently becoming attached 

 to their phycochrome-bearing cells." 



Taking the latter of these alternatives as his starting-point, 

 Schwendener, commencing with the Collemacei, made various 

 observations and experiments, which were afterwards extended 

 to other tribes and genera, the result of which led him to the 



