2yS PAULSON : NOTES on the ecology of lichens. 
.1 ation (Cambridge University Press, 1911), a note as follows was 
appended to the paragraph headed “ Pedunculate Oak-wood 
Association ” :—“ Hornbeam (Carpinus Betulus) is dominant on 
•clay and loamy soils in some parts of south-eastern England ; 
and, since this tree casts a deeper shade than the oak, it is 
possible that the ground flora is affected sufficiently to admit 
of the separation of a hornbeam association.” 
There is a quantity of hornbeam in Hertfordshire and North¬ 
west Middlesex, as well as in Essex. In many of the woods, 
it is coppiced, the oaks being left as standards. In a recent 
article 4 , J. E. Salisbury treats very fully of one section of the 
oak-hornbeam woods of Hertfordshire for the purpose of main¬ 
taining his view that the association should be regarded as a 
•definite sub-type. 
I have found that, where hornbeam is dominant, the lichen 
flora of the Forest differs considerably from that where oaks 
abound. This difference is due not only to the greater amount 
of shade (which is considerably deepened in the Forest as a 
result of lopping in times not very remote) but also to the smooth¬ 
ness of the bark compared with that of the oak. Several 
of the lichens growing upon bark in the hornbeam woods are 
distinctly shade lichens, which belong to the Graphidiaceae. 
The following have been recorded for the Forest hornbeams :— 
Opegrapha herpetica Ach., 0 . atra Pers., 0 . vulgata 
Ach., Gr aphis elegans Ach., G. script a Ach., Phceo graph is inusta 
Muell. Arg., Graphina anguina Muell. Ar g., Enterographa crassa 
Fee., Pyrenula nitida Ach., Parmelia fuliginosa var. Icetevirens 
Nyl., Lecanora snbfusca Nyl., L. allophana Nyl., L. albella Ach., 
Pertusaria leioplaca Schoer., P. Wulfenii D.C., and Thelctrema 
lepadinum Ach. Of the above sixteen, the first eight belong to 
the Graphidiaceae. 
The large number of species recorded is due entirely to the 
persistent efforts of Percy Thompson. They are certainly not 
abundant as individual plants, but there is reason to believe 
that, as the effects of past lopping become less and less inimical 
to lichen-growth, the number of individual plants will increase. 
There is one disturbing factor now' present. The question was 
asked only a short time ago :—What do you think will be the 
effect of the great increase in smoke poured out by the munition 
factories in the neighbourhood of the Forest ? This question 
4 Journal of Ecology, iv., pp. 83-117 (1916 ). 
