STRATOSE THALLUS 



83 



These four types, Zukal finds, are practically without interstices in the 

 tissue and form a perfect protection against excessive transpiration. He adds 

 yet another form: 



5. A cortex formed of hyphae with dark-coloured swollen cells, 

 which is not a protection against transpiration. It occurs among lower crus- 

 taceous forms. 



Hue has summed up the different varieties under four types, but as he 

 has omitted the "fibrous" cortex, we arrive again at five different kinds of 

 cortical formation, though they do not exactly correspond to those of 

 Zukal. A definite name is given to each type: 



I. Intricate : an intricate dense layer of gelatinous-walled hyphae, 

 branching in all directions, but not coalescent (Fig. 44). This rather unusual 

 type of cortex occurs in Sphaerophorus and Stereocaulon, both of which 

 have an upright rigid thallus (fruticose). 



Fig. 44. Sphaerophorus coralloides Pers. Trans- 

 verse section of cortex and gonidial layer 

 near the growing point of a frond x 600. 



Fig. 45. Roccella fuciformis DC. Trans- 

 verse section of cortex near the 

 growing point of a frond x 600. 



2. Fastigiate : the hyphae bend outwards or upwards to form the 

 cortex. A primary filament can be distinguished with abundant branches, 

 all tending in the same direction; anastomosis may take place between the 

 hyphae. The end branches are densely packed, though there are occasional 

 interstices (Fig. 45). Such a cortex occurs in Thamnolia ; in several genera 

 of Roccellaceae — Roccellographa, Roccellina, Reinkella, P entagenella, Combea, 

 Schizopelte and Roccella — and also in the crustaceous genus Dirina. The 

 fastigiate cortex corresponds with Zukal's palisade cells. 



3. Decomposed: in this, the most frequent type of cortex, the hyphae 

 that travel up from the gonidial layer become irregularly branched and 

 frequently septate. The cell-walls of the terminal branches become swollen 

 into a gelatinous mass, the transformation being brought about by a change 



6—2 



