54 THE THALLUS OF THE GENUS PARMELIA, 



development of soredia, and also for comparison with 

 Australian species. 



The mici'oscopic exa,mination was made, and will be 

 set down in order nnder the following heads :■ — (1) Absorp- 

 tion pores; (2a) Upper Cortex; (2b) Lower Cortex; (3) 

 Hyphee; (4) Algse or Gonidia; (5) Rhizinse ; (6) Sperma- 

 gonia; (7) Alliances with other genera. 



For comparison under the last named head, exam- 

 ination was made by means of stained and mounteld serial 

 sections, 3-7^ in thickness of the following species: — 

 Heterodea 'midleri, Nyl., Sticta demutabilis, Krph., S. 

 inilmonacea, Ach., Stictind suborbicularis, M.A., ^S*. reti- 

 r/era, M.A., Physcia Ivyyoleuca, Tuck., Pyrinc cocoes, 

 Evcrnia furfnracea, Mann, and E. 'priinastri, Ach., also of 

 species of Gladonia, Clathrina, CoUema, tiynechohlastus, 

 and Ramalina. In all 192 serial slides Sin. s 1-^-in. were 

 made, each carrying from 30 to 264 serial sections. 



1. AhsoriJtion Pores. 



The first plant examined in detail was ParmeJia 

 tiliacea, Ach., and it was found that the whole thallus wa.s 

 pierced with minute pores with well defined walls, usually 

 presenting a smaller opening on the upper surface of tJio 

 thallus than O'n the under side, as a rule slightly oblique to 

 the parallel cortices, but always simple and unbranchecl. 

 These might well be overlooked, and taken for foldsi in the 

 minute thalline sectiom, did they not repeat themselves on 

 each serial slice, with such alterations in outline as would 

 be expected from parallel sections of a cvlinder. (See 

 Plate II., fig. 1.) 



In the walls of these pores the hyphse usually radiate 

 from the centre upwards and downwards toAvards the 

 outlets, and form the inner lining of the pei'f oration. The 

 algal cells — Cystococcus — lying just beneath the hyphal 

 sheath in the gonidial zone are larger and more closely be- 

 set with hyphae than in any other portio^n of the thallus 

 examined. 



Under an inch objective (Watson) with No. 5 eyepiece, 

 and a magnification of 120 diameters, the pores could be 

 seen in general parallel lines across the section. Under the 

 k objective and No. 5 eyepiece, with a magnificatio'n of 

 720 diameters, the pores show as blotches when the rest 

 of the sectioin is in focus, and the objective has to be fo- 

 cussed down to bring the walls of the pore into perfect 

 view, when the cut edges show as black lines and the rest 



