96 BERNT LYNGE. M.N. Kl. 



The appearances of P. caesia and the subspecies are so different that 

 if there were only a few specimens, it would have been natural to describe 

 them as two different species. But a very rich material, combined with 

 observations in nature, has shown me specimens, which seem to be inter- 

 mediate. 



17. Physcia teretiascula (Ach.) Lynge. 



Parinelia caesia ß tcretiitscula Acharics Lieh. Univ. (1810) p. 479 (p. p.) 

 Physcia caesia var. terctinscida Nyl.ander Lieh. Scand. (1861) p. 112. 



Th. Fries Lieh. Scand. I (1871) p. 141. Wai.xio Adjumenta I (1881) p. 135. 



Crombie British Lichens I (1894) P- 3^^- Boistel Nouvelle Flore des 



Lichens 2® partie 1 1903) p. 73. 



an syn. Physcia leptalea var. subtercs Harmand Lichens de France 



(1909) p. 622; Claud, et Harm. Lieh. Gall, praec. exsic. 319 (sub Ph. 



albiuca). 



Thallus small or middle-sized, orbicular, diam i — 1,5 — 3 cm.; more 

 extensive thalli are often seen, formed by confluent individual thalli. 

 Laciniae appressed to the substratum or only occasionally slightly ascendent 

 at the apices, flexuose, elongate and very narrow (0,2 — 0,3 mm. broad), 

 slightly dilated at the apices, more or less convex, very multifid, 

 repeatedly furcate or pinnate, divaricate and discrete, in young isolated 

 thalli distinctly stellate, later imbricate and sometimes intricate. So red i a 

 white, small and inconspicuous, difform : either scattered over the 

 surface of the thallus or terminal, formed on the lower side of the slightly 

 ascending apices of some laciniae {tenella type). Colour varying from 

 ash-grey to white (not brownish), under side colourless, rhizinae long, 

 dark or even black. 



Thallus covered with an amorphous, uncoloured stratum, 5 — 8 a thick. 

 Upper cortex 25 — 40// thick, dark and opaque at the exterior part, other- 

 wise pale or uncoloured. Hyphae very indistinct, slightly constrictedly 

 septate, spreading in many directions from between the glomerate gonidia, 

 and arranged in contiguous palissades at the exterior part. Medulla white, 

 gradually transformed into the low^er cortex. Lower cortex uncoloured or 

 only locally slightly darkened, hyphae chiefly parallel to the surface. 



Thallus substerile, only a few scattered initiating apothecia without 

 spores. P3'cnides not seen. 



Reaction. Cortex and medulla distinctly yellow by KOH, no co- 

 louring by CaCLOo. 



