IQI6. No. 8. MONOGRAPH OF THE NORWEGIAN PHYSCIACEAE 



pendicular to the surface. They are branched, at least at the base, 

 and the branches sometimes have an oblique direction, interfering with 

 their originally parallel position. If the branching is marked and the 

 hyphae very densely interlaced, a cellular structure is formed. This 

 structure is called plectenchymatous after LiNDAU 1 . The term pseudo 

 parenchymatous is objectionable for the reason that it comprises two 

 textures of very different origins, e. g. the hyphae of fungi and the short 

 (parenchymatous) cells of higher plants. The medullary hyphae are 

 usually loosely interlaced, in rare cases (thin thalli) they are apparently 

 plectenchymatous, e. g. in Physcia sciastrella. A thin section, and a drop 

 of potassium hydrate will show their real texture. 



In Anaptychia the upper cortex is very different from that of Physcia, 

 the hyphae being parallel to the surface, instead of perpendicular The 

 cortex is darker at the exterior than in the interior, but this colour is 

 removed by potassium hydrate, and is merely due to the adspersity of the 

 hyphae. There is no structural limit between the exterior and the interior 

 part of the cortex, and it is not justifiable to reserve the name cortex 

 for the exterior part. Neither is there any definite limit between the 

 cortex and the medulla. Towards the surface, the hyphae are more thick- 

 walled and more densely interlaced, forming a protective stratum over the 

 interior and less resistant textures. In the genus Anaptychia it is, accor- 

 dingly, not necessary to distinguish between a cortex and a medulla from 

 a stratigraphical point of view, and if a distinction should be made, it 

 seems -justifiable to use the term pseudocortex. By this term is then 

 meant an exterior stratum, gradually connected with the medulla without 

 any distinct line of demarcation. 



We should gain a more general point of view of the anatomy of 

 the Lichens on an anatomical-physiological base : The exterior part of the 

 thallus either entirely agrees with the interior part (lower middle-line of 

 the laciniae of most Anaptychia), or it is formed by a protective stratum, in its 

 most original form consisting only of more thick-walled and more densely 

 interlaced hyphae (pseudocortex), in other cases differentiated as a special 

 stratum with a peculiar structure (cortex). 



The first botanists who constructed the anatomy on a physiological 

 base, were SCHWENDENER and his pupils. Their ideas have found a wide 

 application in the study of the vascular plants and in part in that of the 

 algae 2 . It would be very attractive to investigate the Lichen-thallus on this 

 basis, but that is beyond the scope of the present work. 



1 LINDAU: Beitrage zur Kenntn. d. Gatt. Gyrophora, p. 28. 



2 WILLE, N. : Bidrag til Algernes physiologiske Anatomic (1885). 



