1883-84-] Edinburgh Naturalists Field Club. 183 



stratcd that in a Lichen a consortial association is found, — that tlie 

 Lichen is, in fact, made up of Algre ( = gonidia) belonging to various 

 families (Chroococcacea?, JSTostocacere, Palmellacere), Avhich agree to act 

 as hosts to ascomycetous Fungi which are never found alone, although 

 the Algse are capable of existing in a free state, and, Avhen free, of 

 developing normally — that is, of forming zoogonidia or swarm cells, 

 as was first observed by Famintzin and Baranetsky. According to 

 Schwendener, then, the Algte are merely disturbed in their mode of 

 life, although not destroyed, by the Fungi becoming associated with 

 them. At the same time, however, it is to be borne in mind, as Mr 

 Geddes has suggested, that while the Fungus imdoubtedly must 

 obtain its organic food from its tolerant chlorophyllaceous host, by 

 exosmosis of its starch, so that host may derive subsidiary aid from 

 the Fungus by obtaining endosmotically advantage from the nitro- 

 genous waste protoplasmic products of the hyphfe, — ^just as the sym- 

 biotic philozoon is subsidised by similar nitrogenous waste of its con- 

 sortial animal organism, or as insectivorous j^lants like Nepenthes, 

 Sarracenia, or Pinguicula are benefited by the nitrogenous products of 

 insect digestion, or sometimes of insect decay. 



This Schwendenerian doctrine of the constitution of Lichens has 

 been corroborated by the subsequent synthetic experiments of Bornet 

 (" Eecherches sur les Gonidies des Lichens "—' Ann. des Sci. Nat.,' 

 t. xvii., 1873), and Stahl ('Beitriige zur Entwickelungs-geschichte 

 der Flechten,' i., ii., 1877). The former investigator experimented 

 with the common brown-coloured Lichen so abundant on stones 

 about the upper margin of our tidal belt — namely, Parmelia parietina 

 — and found that when Parmelia spores were sown alone, they 

 ramified less and formed no chlorophyll, and that when Proto- 

 coccus was sown alone, it formed no hyplue ; but when the spores of 

 Parmelia were sown with Protococcns, a Lichen (Parmelia parietina) 

 was the issue. Stahl, in like manner, synthetically produced the 

 Lichen, Endocarpon pusillum, which bore perithecia and spermogonia. 

 It may be further remarked that the final shape which a Lichen as- 

 sumes may depend on the gonidia {i.e., the Alga;), as in Ephebe, or on 

 the hyphffi, as in Usnea — the latter being the usual type ; and that the 

 gonidia and hyphte may be equally mingled, when the Lichen is said 

 to be "homoiomerous," or the gonidia may be confined to a single layer, 

 as in Sticta, in which case " heteromerous " Lichens are the result. 



Mr George IMurray has drawn a very interesting jiarallel between 

 certain consortial relationships found in Physoishorid Coelenterates, 

 such as Velella, and in Lichens. In the former, Algte occur in the 

 gonophores or reproductive bells, which have been found to be cap- 

 able of surviving longer — that is, of succeeding better in the struggle 

 for existence — than gonophores devoid of Algpe. So hymenial 

 gonidia — that is, gonidia found in the reproductive cups of such 

 Lichens as Dermatocarpon and Polyblastia — are formed from the 



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