GONIDIA OF LICHENS. 39 



series of experiments with Protococcus viridis, Ag., on which were 

 sown the spores of Parmelia parietina, Ach., with a view of show- 

 ing thai the bypha produced from these spores attached itself to 

 tin 1 isolated cells of the alga, or to small groups of them, rejecting 

 other bodies in their vicinity. 



M. Bornet, in the second place, takes into consideration Alga 

 coloured by phyoochrome, which are distinguished from the pre- 

 ceding, not only by their bluish-green colour, but also by the con- 

 stant absence of a cellulose membrane, properly so called. They 

 are widely distributed, supplying what are known as glaucogonidia, 

 and constituting the greater part of the thalli of Phycolichenes. 

 Their cells are diffused, grouped in colonies, or disposed end to end 

 in moniliform filaments. 



The following are the genera of these alga? met with in lichens : 

 — Calothrix, Ag., furnishes gonidia to Lichina conjinis and 

 pygmea, Ag. Soytonbma, Ag., to Ephebella Hegetschweileri, Itzigs; 

 St reocaulon ramulosum, Sw. (cephalodia) ; Pannaria ht/pomelcena, 

 Nyl. ; P. triptophylla var. nigra, Nyl. ; Cocco-carpia molybdea, 

 Pers. ; Erioderma unguigerum, Nyl. ; P. Dictyonema sericeum, 

 Montg. Lyngbya, Ag., to Stereocaulon ramulosum. Nostoc, 

 Vauch., furnishes gonidia to the following genera amongst the 

 gelatinous lichens : — Collema, Ach., Arnoldia and Physma, Mass.; 

 Leptogium, Fr. ; Obryzum, Wallr. ; and to the cephalodia of 

 Stereocaulon, to Nephromium, Nyl., Stictina, Nyl., and to a certain 

 number of Pannarke amongst the stratified lichens. Stigoxema, 

 Ag., furnish gonidia to Lichenosphceria Lenormandi, Born., 

 Spilonema paradoxum, Born., Ephebe pubescens, Fr., and to 

 the cephalodia of Stereocaulon furcatum, Fr. Glosocapsa, Kiitz., 

 serves to form Synalissa and Omphalaria, D.R., Phylliscum, 

 Nyl , Cora, Fr., and is met with in certain cephalodia of Stereo- 

 caulon. 



M. Bornet says lie lias established the presence of glauco-gonidia 

 in the following 23 genera of lichens : — Ephebella, Itzigs, Lichen- 

 osphcvria, Born.Mscr. ; Spilonema, Born.; Ephebe, Fr. ; Lichina, 

 Ag. ; Synalissa, D.R. ; Paulia, Fee ; Omphalaria, D.R. ; Phylliscum, 

 Nyl.; Collema, Ach. ; Leptogium, Fr. ; Stereocaulon, Schreb. (cepha- 

 iodia) ; Nephromium, Nyl.; Peltigera, Hoffui. ; Stictina, Nyl.; 

 Psoroma, Fr. ; Pannaria, Del. ; Coccocarpia, Pers. ; Erioderma, 

 IV ■ : llrppia, Xa.\g. ; Cora, Fr. ; Dictyonema, Ag. (= Dichonema, 

 X. ;il>. Esnb.) ; Verrucaria, Pers. 



In some species of lichens the hypha predominates in the thallus, 

 there being only a thin stratum of gonidia below the cortical layer ; 

 while in the others the gonidial element predominates. This differ- 

 ence, M. Bornet thinks, corresponds, as a rule, with the mode in 

 which the alga is invaded by the hypha. In the former, the hypha 

 applies itself lather to the surface of the alga than to the interior, 

 destroying its normal form, and giving the appearance of Trente- 

 2)ohlia and Protococcus ; while in the latter, the hypha is projected 



