THE ESSEX FIELD CLUB. 25
Variety of Helix aspersa.—The Secretary exhibited, on behalf
of Mr. E. E. Turner, two specimens of Helix aspersa, destitute of markings.
The snails were from Coggeshall, and were presented to the Museum
by Mr. Turner.
Plates of Mycetozoa Dedicated to Samuel Dale.—Miss G.
Lister, F.L.S., exhibited a copy of Micheli's Nova Plantarum Genera (1729)
for the purpose of pointing out that one of the three plates of the Mycetozoa
was dedicated to Dr. Samuel Dale, of Braintree. Miss Lister gave some
interesting details of the life and work of Micheli, which are embodied
in the notes she has written for the Essex Naturalist (see p. 1).
A Wandering Lichen.—Mr. R. Paulson exhibited specimens of the
lichen, Parmelia revoluta var. concentrica, Cromb., which he called a
wandering lichen because it is found on the grass quite unattached to any
substratum, and is liable to be moved about by the wind when it blows
with any force. This variety of P. revoluta was first found by Sir William
Trevelyan in the autumn of 1855 on Melbury Hill near Shaftsbury, Devon,
and at that time a suggestion was made that certain Parmelias were blown
from trees on to the most exposed part of the hill, and that there they
continued to grow, though liable to be turned over and blown about by
the wind. No recent records of the finding of the plant on Melbury Hill
have been made.
In 1904 D. J. Scourfield discovered this variety on the downs near
Seaford, Sussex, and sent it to friends for the purpose of identification.
No attempt appears to have been made, at that time, to find out more
about its peculiar habit. The plant is now fairly abundant on a small
area of down country near Seaford. Search has been made, this year,
1914, by Somerville Hastings and myself, of the downs between East-
bourne and Seaford, but we have failed to find it anywhere but at the
spot already indicated. The plant readily breaks up in wet weather
so that pieces of all sizes get scattered about on the grass. The larger
pieces are mostly more or less spherical in shape. The outer surface is
rough owing to the manner in which the extremities of the branches
of the thallus are rolled back, thus producing small points. The outside of
a sphere is greenish grey, while the inner, under surface of the thallus
is almost black. The young branches grow over and cover the older ones
so that when cut through the plant exhibits a series of concentric layers.
There are no trees less than three quarters of a mile from the Seaford
station for this plant, and trees are few and far between on this portion
of the downs. On none of the trees in the Seaford area was Parmelia re-
voluta found. After careful search, three flints were seen on which the
lichen was growing, and there is now no doubt whatever that some of the
specimens originated on the flints of the chalk. The plants are fixed by
the rhizinae very loosely and easily break off, especially in wet weather.
After breaking from the stone the lichen gets constantly blown over
and over and gradually assumes the spherical form. There is a point
that still needs explanation; it is this—although small portions of the plant
are blown about from time to time, the area on which it is found at Seaford
is very small. It was the same case with the Melbury plants. The exhibit
included some excellent photographic lantern slides by Dr. Somerville
Hastings.