LICHENS. 



[ 4C6 ] 



LICHENS. 



Endocarpon hepaticum, Pertusaria, Urceo- 

 laria, Opegrapha, &c. 



Eight is generally set down as the normal 

 number of spores in each theca ; but this is 

 not universal here any more than in the 

 Ascomycetous Fungi ; some species of En- 

 docarp<m, Parmelia, &c. have polysporous 

 thecae containing a considerable number, 

 while there are often less than eight. 



Spermogonia. The Lichens exhibit another 

 form of reproductive organs, which are 

 liable to be confounded with Sphceronemei 

 and other Fungi growing on the Lichens, 

 or with parasitical Lichens in similar po- 

 sitions. They form black or brown points, 

 usually near the margins of the thallus 

 (PL 37. fig. 1), and have been found in 

 Borrera, Parmelia, Sticta, Cladonia, Collema, 

 Opegrapha, Spheerophoron, Lichina, JEndo- 

 carpon, &c., and seem to be universal. 



The spermogonia are hollow pustules (PL 

 37. figs. 3 & 13) filled with filaments (sperma- 

 tophores, PL 37. fig. 3) producing extremely 

 minute bacilliform corpuscles (usually sper- 

 matid). They are immersed in the sub- 

 stance of the thallus (PL 37. figs. 2 & 13), 

 and are perceptible externally only by a 

 little projection, if at all; in rare cases they 

 are free and borne above the thallus (some 

 Cladonits, Cetrarice, Gyalecta, &c.). Their 

 ordinary form is globular, ellipsoidal, or 

 irregularly oblong, sometimes sinuous. 

 They have either a simple undivided cavity 

 (PL 37. figs. 13 & 16), or are multilocular, 

 divided in different ways into a variable 

 number of separate chambers or narrow 

 cavities, communicating with a common 

 orifice, the ostiole or pore of the apparatus. 

 This structure bears a close relation to that 

 usual in the Coniomycetous Fungi Cytispora, 

 Septoria, &c., and bears testimony to the close 

 connexion between the Lichens and Fungi. 

 The spermatia are regarded as analogous to 

 the spermatozoids in the antheridia of the 

 higher Cryptogams. 



Pycnidia and Stylospores. Pycnidia are 

 dark-coloured conceptacles, found on Le- 

 cidea and Scutida, resembling the perithecia 

 of the Spheeriee, sessile on the thallus, and con- 

 taining simple filaments (basidia), bearing- 

 isolated spores on their apices (stylospores\ 



The so-called spermogonia and pycnidia 

 appear to be in some cases parasitic Fungi. 



Chemical reagents are useful in the dis- 

 crimination of Lichens. Thus, iodine so- 

 lution will tinge the mature spores or the 

 gelatina hymenea of some Lichens blue, or 

 red without a preparatory blue tinge. So- 



lution of caustic potash produces in the 

 thallu'? of some Lichens a persistent yellow 

 colour, which in others changes to a red ; or 

 if no reaction takes place, solution of chloride 

 of lime produces a red or yellow colour. 

 These reactions must be observed in sections. 



The long-known resemblance of the 

 gonidia of Lichens to numerous forms of 

 the lower Algae, and the similarity of the 

 thecse of Lichens to the asci of Aseomy- 

 cetous Fungi, has of late years given rise 

 to the theory (Schwendener's) that the 

 gonidia of Lichens are really Algse ; the 

 Lichens being Ascomycetous Fungi, living 

 and growing upon them as parasites. The 

 Algae which, according to this view, form 

 the gonidia, are usually species of Palmella, 

 Protococcus, Nostoc, &c., rarely of Confer - 

 vaceae ; and when free, continue to grow 

 and reproduce, still retaining the Alga- 

 form. But when the germinating spores of 

 Lichens come into contact with them, the 

 hyphae surround the cells, enveloping them, 

 and on further growth a perfect Lichen is 

 formed. This question cannot at present 

 be considered as settled ; for while, accord- 

 ing to Bornet, the hyphae never produce 

 gonidia, according to Muller this occurrence 

 most positively does take place. On the 

 whole, it appears that Schwendener's in- 

 genious Lichen-theory will have to be 

 considered one of the modern natural-his- 

 tory romances. 



The Lichens are divided into four families : 



BYSSACEI. Thallus byssaceous or finely 

 filamentous, the granula gonima in a thai- 

 line sheath. 



COLLEMACEI. Thallus gelatinous. 



MYRANGIACEI. Thalamium with cellu- 

 lar cavities, and superimposed theciferous 

 cavities. 



LICHENACEI. Thallus not gelatinous ; 

 variable in colour and form, either filamen- 

 tous, foliaceous, squamous, or crustaceous j 

 gonidial layer usually distinct. 



BIBL. Tulasne, Ann. Sc. Nat. 3 ser. xvii., 

 & Compt. rend. 1851 ; Montagne, Diet, d'hist. 

 nat. 1846 ; Itzigsohn, Bot. Zeit. viii. & ix. ; 

 Flotow, Flora and Bot. Zeit.', Lindsay, Pop. 

 Lichens ; Famnitzin and Boranetzky, Ann. 

 Sci. Nat. se'r. 5, viii. ; Leighton, Brit. Lich. 

 Flora ; Henfrey-Masters, Bot. ; Ny lander, 

 Lichenogr.,Europ., & Flora, 1879 (Jn. Mic. 

 Soc. 1880, 315, colour} ; Reess, Monatsb. fieri. 

 Ak. 1871 ; Bornet, An. Sc. N. 1873, xvii. ; 

 Schwendener, NageWs wiss. Bot. 1860, '62, 

 '68, SiAlgentyp. Flecht. Gonid., 1869; Archer, 

 Jn. Mic. Soc. xiii., xiv (all the papers on 



