96 
REPORT ON THE LICHENS OF EPPING FOREST. 
these extreme conditions, the lichen, while not actually succumb 
ing to its inclement environment, is compelled to suspend its 
growth until the return of more favourable seasons ; and so its 
rate of growth is slow. In moist warm climates, where lichens 
attain their greatest development, external conditions are 
favourable to much more rapid development ; but here, un¬ 
fortunately, we have as yet no data as to rate of growth. But 
even in our own temperate latitudes it is evident that the 
extremely slow development claimed for lichens does not always 
hold. When we meet with fruiting lichens, overspreading 
decaying leaves, which can scarcely have lain on the ground 
more than two or three years, others growing on old boots, or 
on dung, and fruiting freely, others overspreading growing 
mosses ; and when we notice, as we do sometimes, that on an 
old wall the best developed lichens are growing, not on the wall 
itself, but on the cement jointing which was added when the 
wall was last repaired, perhaps 20 years before ; we begin to 
suspect that, after all, under more equable conditions of tem¬ 
perature, and in a humid atmosphere, the rate of growth of 
some lichens at least must be far more rapid than has been 
generally assumed to be the case. We know one mass of con¬ 
crete at They don Bois, surrounding a surface-water drain 
which was formed in 1903, and which, in 1910, after only seven 
years, was covered with Lecanora galactina in abundant fruit ; 
and a Portland stone garden-ornament, new in 1904, was, in 
1910, after only six years, covered with patches of a fruiting 
Verrucaria (probably nigrescens). It is perhaps noteworthy 
that these forms have always a very scanty development of 
thallus and produce their fruit very freely. 
ENEMIES AND PROTECTIVE RESEMBLANCE . 
We have now to enquire what are the enemies with which 
Lichens have to contend in our Forest. 
Mites of the family Oribatidce must be reckoned among the 
chief foes of these plants, upon which they feed, seeming to have 
a special predilection for the ripe fruits. We have had excellent 
specimens of Physcia parietina spoiled by hidden mites of this 
family,which have eaten out the contents of the mature apothecia 
after the lichens have been gathered. One can sometimes 
see small flocks of the mites browsing upon the thallus of tree- 
