2OI 



representatives which came to my notice have been included under 

 Pannaria as P. microphylla, P. nigra and others. The algae and 

 spore-characters at once indicate that these species can not be includ- 

 ed in Pannaria nor are the genera even closely related. 



The thallus is crustaceous as to its macroscopical appearance. 

 On making sections it is, however, found that a well-marked upper 

 cortical layer is quite constantly present, which is dark in color, due 

 to a deposit of coloring substance in the cell-walls. The algal layer 

 is also well developed and consists of the alga Rivularia nitida with 

 its usual gelatinous covering through which the hyphal cells extend. 

 Haustoria proper are not present ; the medullary tissue consists of 

 rather short-celled, somewhat frequently branching hyphae which are 

 continuous below with the dark rhizoidal hyphae. 



As indicated, the color of the thallus is dark ; this is true of all 

 the species which came to my notice ; close examination with a 

 hand lens will reveal the fact that the higher forms tend to become 

 foliose, the thallus consisting of very minute scaly lobules, dark 

 above as well as beneath ; these lobules are cortical above and below. 



The apothecia are of medium size, sessile or partially immersed in 

 the thallus ; the disk is flattened, the epithecium brown to dark ; the 

 hypothecium is usually of a brown coloration, sometimes blue-black ; 

 the spores are few, variable in size and form, due to the fact that but 

 few attain maturity. When mature they are oblong, colorless and 

 four-celled ; it may, however, be possible that they become colored, 

 though none such came to my notice. It need scarcely be stated 

 that a true thalloid exciple is not present. 



The few representatives so far as known in this country occur in 

 the north temperate zone and the arctic regions ; they seem to live 

 normally upon rock or coarse sandy soil. 



PLATE 15, fig. 10. 



LECOTHECIUM NIGRUM (Huds.) 

 Paraphyses and spore-sac with two-celled immature spores. 



3. LICHINA Ag. Syn. Alg. Scancl. xii. 1817. 

 This interesting group of lichens has been erroneously placed by 

 various authors, owing to the fact that the histology was not suffi- 

 ciently known. On account of the dark minute much-branched thallus 

 it has been placed near Ephcbc ; again, because of the more or less 



