196 LINDSAY, ON LICHENS. 



cases, naked and sessile, seated on the surface of the hori- 

 zontal thallus, or forming the terminations of the ramuscles 

 in the erect fruticulose one. The immersed and semi- 

 immersed spermogones are plunged in the substance of the 

 medullary tissue of the thallus, and they are usually partly 

 covered by the cortical layer, and partly encircled by the 

 gonidic layer." 



The other organs to which he more especially calls atten- 

 tion in this memoir are the Pycnides. These are described 

 as follows : 



" The Pycnides of lichens may be described generally as 

 externally resembling in form, colour, site, &c, the spermo- 

 gones, from which they can be distinguished only by micro- 

 scopical examination. The essential difference lies in the 

 character of the contained corpuscles — the stylospores, though 

 the sterigmata also differ from those of the spermogones to 

 this extent, that they are almost always simple, shortish, and 

 stoutish, generating the stylospores only at their apices. The 

 pycnides consist, like the spermogones, of a — 1. Capsule; 2. 

 Nucleus, made up of sterigmata, with stylospores instead of 

 spermatid however ; 3. Cavity ; and 4. Ostiole. They re- 

 semble outwardly, and are frequently mistaken for — a. Sper- 

 mogones ; b. Minute Verrucarias ; c Parasitic Fungi ; and 

 d. Parasitic Lecidea, such as those mentioned under the head 

 of spermogones. From all of these bodies they can only be 

 distinguished by careful microscopical examination. 



"They resemble the organs known as Phoma, Septoria, 

 Diplodia, &c, which, according to Tulasne, belong, as secon- 

 dary reproductive organs, to various thecasporous fungi. 

 Their occurrence, alike in fungi and lichens, is a strong link 

 binding together in close alliance these two great cryptogamic 

 families. They are more plentiful in the lower than in the 

 higher. — in crustaceous than foliaceous, lichens, — or, in other 

 words, in those species most nearly approaching, in other 

 particulars of their organization, the fungi. In crustaceous 

 species they usually occur as very minute, black perithceia, 

 resembling the apothecia of Verrucaria. But in the higher 

 lichens, they are frequently much larger, more closely 

 resemble the spermogones, and arc variously coloured, as in 

 Peltigera and Alectoria. In the first-named genus they are- 

 marginal, like the apothecia; in the other, they are stated 

 sometimes as warts on the thalline filaments, or in the :i\ils 

 of their ramifications. 



" Pycnides are sometimes associated both with spermogones 

 and apothecia ; sometimes with apothecia alone, no spermo- 

 gones being present. Occasionally, pycnides and spermogones 

 occur without apothecia, as in some species of Singula ; and 



