40 i INTRODUCTION TO CRYPTOGAMIC BOTANY. 



fniit is at first closed, and in Gyropliora the disc is in a man- 

 ner proliferous, and produces a number of partial discs on the 

 original hymenial surface. As in other cases, the cells from 

 whence the asci spring belong to the medullary stratum ; the 

 border, on the contrary, to the cortical. The thallus is always 

 foliaceous, and more or less peltate, though becoming ex- 

 tremely dry and brittle when exposed to drought. Several 

 of the species have tufts of strong rootlets, by which the frond 

 is attached more firmly to the rock, and some have deep pits, 

 with which swellings in the upper surface correspond, from 

 whence they have received, in the country where they most 

 abound, the popular name of Tripe de Roche. They afford, 

 however, at best, a very poor kind of food, and, in fact, are so 

 apt to disagree that they are quite ineligible. One fine 

 species exceeds sometimes a foot in breadth, and many of them 

 are rather striking forms. The convoluted perithecia are 

 analogous to Gloniurni, to a small patch of which they bear a 

 close resemblance. Indeed, though there are occasionally 

 orbicular shields, their affinity is rather with Graphis than 

 with Lecidea. Umbilicaria is a Gyrophora without the con- 

 volute discs. Pyxine, Fr., is distinguished by its Parmelioid 

 thallus, orbicular perithecia, opening by a circular aperture, 

 and waxy disc. The sporidia vary considerably in size and 

 appearance. In Uimhilicaria pustidatct they call to mind 

 those of Hysterium elongatum, but are more comphcated 

 and larger, while in Gyrophora proboscidea they are very 

 small, with a smooth epispore. In both, Tulasne finds minute 

 oblong or linear spermatia, springing from the point of junc- 

 tion of the cells, which compose the moniliform threads, which 

 line the cavity of the spermatogonia. The genera Gyrophora 

 and Umbilicaria have their principal seat in arctic Europe 

 and America, where they abound under various f(frms. Species 

 also occur in temperate Europe and America, and in alpine 

 tropical America, especially in Peru and in the Himalaya 

 mountains, mostly at high elevations. They are exceedingly 

 rare in the temperate and frigid regions of the south. One or 

 two species are found at the Cape, and another in the Falk- 

 land islands. Omphalodium, Meyer (Sticta Hottentotta), 



