55 



5- THE CEPHALODIA. 



Various outgrowths from the lichen-thallus had been observed by 

 several authors previous to Acharius. These outgrowths included 

 true cephalodia as well as secondary thalloid formations and were 

 variously designated as corpuscula, macula?, etc. Acharius (1803) 

 first proposed the term cephalodium and rightly applied it (in the 

 sense of Forssell) in the lichen-species Pcltigera aphthosa. Florke 

 (1819) designated them sponge-like outgrowths (corpuscula fun- 

 gosa) and gave a fairly accurate description of them as they occur in 

 Stereocaulon and Pilophorns robnstiis. Wallroth describes them 

 under the name phymata and emphasizes the fact that they differ in 

 structure as well as in color from the normal thallus ; he classified 

 them as to form. Fries (1857) described their external appearance 

 quite accurately, but did not understand their true nature and origin ; 

 he believed that the gonidia of the cephalodia were subject to varia- 

 tion in color and form. Nylander considered the cephalodia as 

 pathological or parasitic structures, and pointed out the difference 

 between the normal gonidia of the thallus and the gonidia of the 

 cephalodia. Schwendener, Bornet, Babikof and others studied these 

 structures without making, however, any important additions to the 

 work done by Nylander and Fries. Winter (1877) gave us the first 

 more accurate descriptions of the cephalodia as they occur in Sticta 

 and Solorina. Minks (1879) describes the cephalodia as " gonotro- 

 phies " and expresses the opinion that they are of wide occurrence ; 

 he states that they are constantly present in Lecanora gelida, Stereo- 

 caulon ramulosum and Peltigera aphthosa. Branching cephalodia 

 occur regularly upon Sticta amplissima found in Europe, while they 

 are regularly absent in our American species (Forssell). By far the 

 most complete and important discussion of this subject is that by 

 Forssell. This author made a careful study of their origin, develop- 

 ment and distribution. The student is referred to his original commu- 

 nication as it appears in Flora for 1884 ; his classification is as follows : 

 I. Cephalodia z'cra (organically connected with the normal lichen 



structure). 



A. Ccph. cpigcna ( pcrig'cna) (occuring upon the upper sur- 

 face of the thallus). 



1. Ccph. tnbcrcnJosa (Peltidea aphthosa). 



2. " lobnlata (Sphaerophorus stereocauloides). 



3. " clcrcata (Stereocaulon ramulosum). 



