and the causes affecting its recent diminution. 73 
existed there, or be found only in an ill-developed or abnormal 
condition. Now, owing partly to the trees in most parts of 
the Forest being at present too crowded and grouped together, 
partly to the large quantity of scrub and undergrowth 
surrounding their stems, and partly to the frequent and 
general pollarding of the hornbeams, neither sunlight nor 
rain can find such immediate and direct access to their 
trunks and branches as lichens essentially require for their 
due evolution. 6 But for these adverse influences we might 
have expected that the spores or soredia of such species and 
varieties as grow upon the old and felled trees would have 
germinated and gradually developed into perfect plants on 
the other trees growing in their neighbourhood. This, 
however, generally speaking, is by no means the case, and 
it is only on the more isolated trees, occurring in open 
situations, exposed to sunshine, wind, and rain, that any 
well-developed lichens are to be found. 7 For though, as 
already observed, the longest-lived of all vegetables, lichens 
are at the same time so delicately constituted that, if the 
atmospherical conditions under which they grow are in any 
way interfered with, those already developed immediately 
begin to decay, and those in the process of development 
speedily perish. Hence, instead of finding the trunks of the 
trees covered with these “ creatures of light and air,” we 
usually find only protohypbse of species of Pyrenomycetes 
and various algals, such as Protococcus —the “creatures of 
damp and shade.” 8 
6 Thus also is it that the birch, and more especially the holly, which 
elsewhere yield a considerable number of species are here so destitute of 
almost any trace of lichen-growth. 
7 It is to be observed that, though lichens greedily imbibe water for 
then nourishment, yet when this is not naturally and in due course dried 
up by the sun and wind having free access to their substrata, it becomes 
injurious to the life of such species as are not aquatic or semi-aquatic. 
8 According to Schwendenerism, it is just in these circumstances when 
we have the fungal mycelia ready to lay hold upon the algals, that 
lichens would be found in various stages of evolution. Facts, however, 
are in direct antagonism to this hypothesis; and so far from lichens 
being thus manufactured, I have repeatedly observed in the Forest that 
when the pro-mycelium of Pyrenomycetes comes into contact with and 
invests in its meshes the Protococcus , the latter is speedily destroyed. 
