SPERMOGONIA 195 



better lighted portions of the thallus. On the fronds of foliose forms, they 

 appear, for instance, on the swollen pustules of Umbilicaria pustulata, while 

 in Lobaria pulmonaria, they are mostly lodged in the ridges that surround 

 the depressions in the thallus. In Parmelia conspersa, Urceolaria (Diplo- 

 schistes) scruposa and some others, they occasionally invade the margins of 

 the apothecium or even the apothecial disc as in Lichina. Forssell' found 

 that a spermogonium had developed among cells of Gloeocapsa that covered 

 the disc of a spent apothecium of Pyrenopsis haematopis. 



In fruticose lichens such as Usnea, Ramalina, etc. they occur near the 

 apex of the fronds, and in Cladonia they occupy the tips of the ascyphous 

 podetia or the margins of the scyphi. In some Cladoniae, however, spermo- 

 gonia are produced on the basal squamules, more rarely on the squamules 

 that clothe the podetia. 



b. Form and Size. Spermogonia are specifically constant in form, the 

 same type being found on the same lichen species all over the globe. The 

 larger number are entirely immersed and are ovoid or roundish (Fig. 1 1 1 A) 

 or occasionally somewhat ^■aXXe.r\&^\iodS&s(Nephroiniu'm laevigatum),or again, 

 but more rarely, they are irregular in outline with an infolding of the walls 

 that gives the interior a chambered form (Fig. 1 1 1 B) (Lichina pygmaea) ; but 

 all of these are only visible as minute points on the thallus. 



B 



Fig. III. Immersed spermogonia. A, globose m Parmelia 

 acetabulum Dub. x 600 ; B, with infolded walls in Lecidea 

 (Psora) testacea Ach. x 144 (after Gliick). 



A second series, also immersed, are borne in small protuberances of the 

 thallus. These very prominent forms are rarely found in crustaceous lichens, 

 but they are characteristic of such well-known species as Ramalina fraxinea, 

 Xanthoria parietina, Ricasolia amplissima, Baeomyces roseus, etc. Other sper- 

 mogonia project slightly above the level of the thallus, as in Cladonia papillaria 

 and Lecidea lurida; while in a few instances they are practically free, these 

 last strikingly exemplified in Cetraria islandica where they occupy the 

 small projections or cilia (Fig. 1 1 2) that fringe the margins of the lobes ; they 

 are free also in most species of Cladonia. 



' Forssell 1885. 



13—2 



