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



occasionally cellulose *), the gonidia are often seen attached to 

 the radicles of the lichenohyphse of its exterior portion. This 

 attachment, however, is in no way genetic or parasitic, nor does 

 it argue any kind of " copulation " whatever, as Schwendenerism 

 affirms. The gonidia are in fact neither adnate to nor penetrated 

 by the myelohyphse t, but only adherent to them by means of 

 the lichenin, with which all the different elements of the thallus 

 are penetrated. This holds good equally in the case of unstratified 

 thalli, where lichenohyphse are present, as amongst the Collemacei 

 and the lower genera of the Lichenacei. In all such instances, 

 the apparent copulation is simply an amylaceous adherence, and 

 the fancied penetration the result of erroneous observation, or of 

 an abnormal condition of the gonidia. 



Such, then, is the undoubted origin of the gonidia in, and their 

 relation to, the rest of the lichen-thallus. To trace this in every 

 instance from the germinating spore to the perfect thallus 

 throughout the various families and tribes, is by cultivation 

 apparently impossible, and in nature itself by no means an easy 

 matter. There can, however, be no doubt that what is true in 

 the above instances is true also in all others. For as Schwen- 

 dener, while predicating the same phenomenon witnessed by 

 Beess for all the lichens in general, whose evolution he himself 

 had studied, rightly affirms (in Eror. zur Gonid.), " It is incon- 

 ceivable that a plant should become developed at one time in one 

 way, and at another time in one completely different." Hence in 

 the Collemacei, the stronghold of Schwendenerism, where it is 

 more difficult to trace the progressive evolution of the thallus, it 

 is evident that the assumed algo-fungal-licheu phenomena seen 

 by its supporters must be interpreted in accordance with the 

 well ascertained facts now brought under your notice. But even 

 in these we are not quite left without the means of satisfactorily 



* In the cellulose medulla also, as in Psoroma hypnorum, the gonidia are 

 seen to be produced in the interior of the cellules, just as they are in those of 

 the cortical stratum. 



t Treub, who specially investigated this point, never saw the hyphal ex- 

 tremities penetrating into an uninjured gonidium — still with contents; nor 

 from their nature can they have any such power of penetration. Indeed, as 

 has been welt observed by Mr. Archer (Trans. Journ. Micr. Sc. n. s. xiii. p. 234), 

 Bornet's researches on the subject, which showed in certain cases the hypha 

 destroying the gonidium {vide p. 263), prove too much in so far as Schwen- 

 denerism is concerned, inasmuch as Schwendener's parasite does not destroy, but 

 rather stimulates. 



