2l6 



PHYSIOLOGY 



published an account of various oil-cells in a large series of calcicolous 

 lichens (Fig. 117). 



The occurrence of oil- (or fat-) cells is not dependent on the presence of any 



particular alga as the gonidium of 

 the lichen. Funfstiick 1 has described 

 the immersed thallus of Opegrapha 

 saxicola as one of those richest in 

 fat-cells. The gonidia belong to the 

 filamentous alga Trentepohlia um- 

 brina and form a comparatively 

 thin layer about 160 p thick near 

 the upper surface; isolated algal 

 branches may grow down to 350/4 

 into the rock, while the fungal ele- 

 ments descend to 1 1*5 mm., and 

 though the very lowest hyphae were 

 without oil as were those imme- 

 diately beneath the gonidia the 

 interlying filaments, he found, were 

 crowded with oil-cells. Sphaeroid 

 terminal cells were not present. 



Funfstuck 1 has re-examined the 

 thallus of Petractis exanthematica, 

 an almost wholly immersed lichen 

 with a gelatinous gonidium, a species 

 of Scytonema. The thallus is homoio- 

 merous : the alga forms no special 

 zone, it intermingles with the hy- 

 phae down to the very base of the 

 thallus; the hyphae are extremely 

 slender and at the base they measure 

 only about l/t in width. Oil-cells 

 are abundant in the form of inter- 

 calary cells about 3-5 /* in thickness. Nearer the surface sphaeroid cells 

 are formed on short lateral outgrowths; they measure 14-16/4 in diameter 

 and occur in groups of 15 to 20. The superficial part of the thallus Is a 

 mere film ; the hyphae composing it are slightly stouter and more thickly 

 interwoven. 



Bachmann 2 and Lang 3 have further described the anatomy of endolithic 

 thalli especially with reference to oil-cells, and have supplemented the 

 researches of previous workers. New methods of cutting the rock in thin 



'* Fiinfstuck 1899. 2 Bachmann I9O4 1 . 3 Lang 1906. 



\ 



A B 



Fig. 117. Lecidea imniersa Ach. A, sphaeroid 

 fat-cells from about 8 mm. below the surface 

 x 550. B, oil-hyphae in process of emptying : 

 a, sphaercid cells containing oil ; l>, cells with 

 oil-globules x 600 (after Funfstiick). 



