lIOHENBB. 305 



402. — The gonidia sometimes escape from the thallus of 

 the hchen surrounded with a few liyphse (Fig. 211) ; these 

 are called soredia. Under favorable circumstances they may 

 giye rise to new lichens, and hence have been looked upon 

 by some as asexual organs of reproduction. Soredia are, 

 however, rather of the nature of buds or gemmae, which, 

 under certain circumstances, become detached. Their pro- 

 duction is, to a certain extent, accidental. 



(a) 1. The Nature of Gonidia. Uiitil recently, the gonidia of 

 lichens have been generally regarded as accessory reproductive bodies. 

 De Bary,* however, in studying the Colleniacese, and noting the remark- 

 able resemblance between their gonidia and certain algse, came to the 

 following conclusion : ' ' Either the lichens in question are the perfectly 

 developed states of plants whose imperfectly developed forms have 

 hitherto stood among the algse as the Nostocaceae and Cliroococcacese , 

 or the NostocacesB and Chroococcaceae are typical al<ias which assume the 

 form of Collema, EpJiebe, etc., through certain parasitic Ascomycetes 

 penetrating into them, spreading their mycelium into the continuously 

 growing thallus, and becoming attached to their phycochrome-contain- 

 ing cells." Schwendener,f Reess.j: and Bornei§ have taken up the 

 second theory in the above alternative, and extended it to all lichens. 

 Schwendener, who first made the definite statement of the theory, holds 

 that every lichen is a colony composed of a parasitic fungus on the one 

 hand, and a number of low algse on the other ; the former, which pro- 

 duces the asci, spermatia, and other reproductive bodies, is nourished 

 by the latter, whicli constitute the gonidia of tlie lichen. 



A lichen, according to this view, is not an individual plant, but rather 

 a community made up of two kinds of individuals ; and the gonidia are 

 only the temporarily imprisoned algae, which furnish nutriment to the 

 parasitic fungus. The fungus parasite does not differ in any essential 

 character from those of the two higher orders of the Ascomycetes. 

 Leville, in speaking of lichens and the ascomycetous fungi, said,|| 

 " I find the distinctions to be so trifling, that I have always regretted 

 that these vegetables should not be placed under one head. The para- 

 physes, thecse (asci), and spores are identical. " 



* " Morphologic und Physiologie der Pilze, Flechten, und Myxomy 

 <>eten,"1865, p. 291. 



f Dr. S. Schwendener : " Unterauchungen Tiber deu Flechtenthallus," 

 1868, and " Die Algentypen der Flechtengonidien," 1869. 



X Professor Max Reess : " Ueber die Entstehung der Flechte Oollema 

 glaucescens," etc , 1871. 



§ Dr. E. Bornet : " Recherches sur les &onidies des Lichens," 1873. 



[ A letter to Decaisne, as given in Le Maout and Decaisne's " Traite 

 Generale de Botanique," 1868. 



