Rock Lichens 
pile of the ila and these no doubt distribute 
its spores. 
But the interesting pate about chroolepus is that this 
minute growth of ¢th to »,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 algz, 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 animalcule 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 alge 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. 
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