Rock Lichens 



pile of the chroolepus, and these no doubt distribute 

 its spores. 



But the interesting point about chroolepus is that this 

 minute growth of ith to y^th of an inch is like a 

 miniature heath, and forms a very complicated little 

 association of its own. 



Each little upright branching alga with rich golden- 

 brown or orange twigs rises out of a sort of turf com- 

 posed of dead algae, fungi, insect-corpses and dust. 



Here and there one sees a fallen chroolepus "tree" 

 lying on the turf and covered or encrusted by slate- 

 coloured fungus filaments, green cells of Pleurococcus 

 and the like. It has an odd resemblance to a fallen log in 

 a wood covered with mosses, ferns, and flowering plants. 



Swarms of bacteria also occur in the basal turf. If 

 one could get a mind small enough to appreciate the 

 chroolepus heath, it would be indeed a weird and 

 wonderful place. It is submerged (like the Amazon 

 valley) in heavy rain, and one would then see the brilliant, 

 pear-shaped, orange-brown spores violently hurling 

 themselves about through the branches by means of 

 their double whiplike processes.* There are Nema- 

 tode worms like great pythons crawling through it : 

 strange transparent sluglike animalculae are perceived, 

 on intrinsic evidence, to have been grazing on the 

 branches. The parasites on the trentepohlia are 

 varied and beautiful. Gold-brown, artificial-looking 

 diatoms and green algae are wrapped round some of 

 them, and the slender deadly threads of parasitic fungi 

 creep and twine everywhere. 



But as the reader can quite well examine such 

 trentepohlia associations for himself, it is unnecessary 

 to give more details. 



* The motion is difficult to describe. If one cracks a long Australian stock- 

 whip, it is difficult to keep one's feet. The spore lets itself go. 



6 4 



