RECENT RESEARCHES INTO THE NATURE OF LICHENS. 147 



of spores,^ and four by gonidia with (soredia) or without hyphse. 

 The fact that a lichen-thallus may be developed from cells which 

 do, as well as from cells which do not, contain chlorophyll estab- 

 lishes, he considers, the autonomy of the Lichens. 



Of the publications which afford evidence in favour of Sch- 

 wendener's theory the first is that of Borzi.~ In it an account 

 is given of numerous " culture" experiments made with various 

 Lichens, such as Parmelia jmlveridenta, Physcia ciliaris, and 

 others. The conclusions to which the observations led were the 

 following: (1) that the gonidia stand in no genetic relation to 

 the hyphse, but that on the contrary they are autonomous 

 organisms, true Algse, which serve as hosts for the hyphse; 

 (2) that the relation between the hyphseand the gonidia is always 

 such as exists between a Fungus and the substratum upon which 

 it lives; and (3) that Lichens consist of ascomycetous Fungi 

 parasitic upon their gonidia, which are true Algee. 



An important contribution to the discussion is the paper by 

 Bornet.^ He begins by giving some account of cases observed 

 by him in which the gonidia of certain Lichens reassumed their 

 algal condition. In certain old thalli of Opegraplta varia — the 

 gonidia of which are furnished by filaments of Trentepohlia 

 (Chroolepus) — he found that the gonidia had here and there 

 regained their normal structure. They had become elongated 

 and had produced numerous sporangia, such as are peculiar to 

 the genus Trentepohlia, and numerous zoospores could be de- 

 tected moving amongst them. These fertile filaments were dis- 

 tinctly continuous with those which were still acting as the 

 gonidia of the Lichen. Again in Fannaria triptophijlla , JSijl. 

 var. nigra, he frequently found projecting from the tubercles of 

 the thallus which had become ruptured, filaments which were 

 evidently prolongations of the mass of bluish gonidia contained 

 in the thallus of this species. These observations convinced him 

 that the two kinds of gonidia in the thallus of this Lichen, 

 though so different in appearance, are really two forms of the 

 same Alga. The filamentous gonidia are but slightly modified 

 forms, but in the spherical gonidia the original normal algal form 

 is no longer recognisable. 



Further, the thallus of Collema, as is well known, becomes 

 covered under certain circumstances with great numbers of 

 small round grains, produced from the extension and development 

 towards the exterior of a fold of the gonidial filaments. Usually 



^ He states that he has observed in Sphieromphale the direct develop 

 merit of gonidia from spores {^i). 



2 'Intorno agli olBci dei gonidi de'Licheni, Estr. dalla Scienza contem- 

 poranea, Palermo.' Reprinted in ' Nuov. Giorn. bot. Ital.,' 1875. 



^ " Deuxieme note sur les gonidies des Lichens," 'Ann. Sci, Nat.,' ser. 

 V, t. xix. 



