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8. DERMATOCARPON Eschw. Syst. Lich. 21. 1824. 



This genus, considered from a morphological standpoint, forms 

 the connecting link between Verrucaria and Endocarpon. Phyloget- 

 ically it does not seem to be derived from Verrucaria, as is indicated 

 by a marked difference in the spore-characters. It is more than 

 likely that these two genera are represented by two different fungal 

 ancestors derived from some generic groups of the Sphaeriaceae. 



The description of this genus is based upon the characters occur- 

 ring in the only well-known representative, namely, Dermatocarpon 

 pusilhim, usually included in Endocarpon. 



In D. pusilhim the thallus, though very minute, is typically foli- 

 ose. There is present an upper cortical layer, an algal layer, a 

 medullary layer, but no true lower cortical layer, its place being 

 taken by a layer consisting of a more dense network of hyphal tissue 

 whose cell-walls are dark colored. The thallus, consisting of a 

 single entire lobe, is held to the substratum by numerous rhizoids. 

 As a rule, the thalli occur in clusters of five to twenty or more ; more 

 rarely they occur isolated over the substratum. The algae (Pleuro- 

 coccus vulgar is} are quite numerous and are arranged in a manner 

 typical of this alga when occurring in the lichen-symbiosis, that 

 is, they occur in vertical more or less irregular rows, closely sur- 

 rounded by the semi-cortical hyphal tissue. 



The apothecia are very small, usually one on each thallus. They 

 are immersed in the thallus opening by an irregular pore in its super- 

 imposed tissues (algal layer and upper cortical layer). The hypothe- 

 cium is dark and shows a tendency to become cortical. The para- 

 physes are almost entirely gelatinized, as are also the spore-sacs. 



The genus is at once recognized by its spore-characters. In 

 Verrucaria and the related group, Endocarpon, the spores are sim- 

 ple, colorless and eight in each spore-sac, while in Dermatocarpon 

 as represented by D. pusilhim there are from one to three colorless 

 more or less ovoid multilocular spores. It may, however, be possible 

 that there are species of Dermatocarpon with eight spores in each 

 spore-sac. Further careful revision of Verrucaria, Staurothele, 

 Dermatocarpon and Endocarpon will reveal whether this be so or not 

 and also whether all species of Dermatocarpon have foliose thalli. 



Another character constantly met with in D. pusilhim is the pres- 

 ence of thecial algae, which are ejected with the spores to which they 

 adhere (see discussion of Thecial Algae). 



