894- INTRODUCTION TO CRYPTOGAMIC BOTANY. 



certiiinly analogous. The external coat is a mere modification 

 of the cortical stratum, though often somewhat differently 

 coloured, as the inner substance is of the medullary stratum. 

 The other genera belonging to the group are of comparatively 

 small importance. Of these, Porodothion, Fr., is distinguished 

 by the absence of true perithecia, insomuch that it is exactly 

 analogous with Dothidea. SjDhctirompliale has coloured soli- 

 tary perithecia, and approaches very near to Verrucaria. The 

 species are European, and live on rocks. The coloured peri- 

 thecia prevent their being considered simple Trypethelia. 

 Astrothelium has a multilocular pustule from the confluence 

 of the perithecia, which have a common ostiolum, analogous 

 with Cytispora. Trypetheliei are very nearly confined to the 

 tropics, but there are one or two species in the southern 

 hemisphere, and Tryjoethelium cruentum has been sent to 

 me from South Carolina, on the bark of Ilex opaca. 



3. Verrucariei, Fr. 



Excipulum closed, resembling the perithecium of a 8plui3ria, 

 discharging the sporidia by a central ostiolum or pore. Thallus 

 crustaceous. 



432. Verrucariei are distinguished by their simple peri- 

 thecia, which are not immersed in any distinct pustule of the 

 crust. In Pyrenastru7n, the perithecia are crowded round a 

 common column very much after the fashion of a circinating 

 Sphcerla, and in other cases they are slightly crowded ; but 

 the distinction holds generally good. For the most part, the 

 walls of the perithecia are black. The thallus, when pre- 

 sent, is crustaceous ; but in some cases it is so thin, and con- 

 fluent with the substance of the matrix, as to be inseparable 

 and almost indistinguishable. The sporidia are in general far 

 less complicated than in the preceding group. The species 

 often occur on the living bark of trees, but they are found also 

 on mould, or upon the hardest rocks. One species, at least, 

 inhabits the smooth stones of running streams. As remarked 

 above, the resemblance to Fungi is very close, and this is not 

 confined altogether to the simpler species. A Cryptogam re- 

 sembling Pyrenastrum, occurs on the smooth bark of oaks 

 in Northamptonshire, and has been found also by Mr. Spruce 



