LICHENS. 137 
These all increase, till in unnoticed years 
The sterile rock as grey with age appears, 
With coats of vegetation thinly spread, 
Coat above coat, the living on the dead ; 
These then dissolve to dust, and make a way 
For bolder foliage nursed by their decay.’ 
Precisely the same effects are produced on the 
newly-formed coral islands of the Pacific. The 
winds or the waves waft thither the invisible spore 
of some lichen that may have had its birthplace 
on the rocks of the far-off Andes ; it finds a rest- 
ing-place, and the few simple circumstances neces- 
sary for its development, in some sheltered nook 
where the dashing waves have ground the coral 
into glittering sand ; and through course of time 
it assumes a crust-like appearance, puts forth its 
organs of fructification, and sows around it a 
colony of similar individuals. These harbour the 
wind-wafted soil beneath their tiny leaves, and 
form, by their decomposition, a layer of mould to 
which new species are day after day adding their 
decaying tissues, until at last a sufficient soil has 
been deposited for the growth of the ferns, the 
bread-fruit, and cocoa-nut trees that have been 
wafted from the neighbouring- islands. And thus, 
through the agency of an all but invisible seed, 
developed into the lowliest form in which it is 
possible to conceive that life can be maintained, 
what was once a barren, solitary islet, where no 
