PAULSON : NOTES ON THE ECOLOGY OF LICHENS. 283
if he had made any observations on the rate of growth of these
plants, he sent me in one of his letters the following :—
" On the border tiles (stone, slate, with much mica), in my
garden, are many fine specimens of Squamaria saxicola. These
are very rapid growers and develop as much as 2.5 cm. within a
few months. They soon come into bearing apothecia, but as
a rule do not last more than two or three years, soon becoming
abraded in the centre, then gradually dying away, to be replaced
by new plants. I have known this species in one situation
(one single plant only) for 25 years. It never seems to increase
in the slightest and is always full of apothecia. It occurs on
a sandstone step of a stile leading into a field from the main
road over which I should think 50 to 100 people pass daily,
and does not appear to have suffered any accident all that time."
" Many Verrucariae growing about the outlets of drains, on
backyard tiles, and in such places, and a depauperated form of
L. coarctata, though well fruited, appear to be annual growths."
Since I last exhibited a series of photographs that threw
some light upon the rate of growth of lichens, there has
appeared a paper entitled "The Rate of Growth and Ecesis in
Lichens "* by Bruce Fink. He gives the results of a series of
measurements of the rate of growth of various lichens taken at
two well-separated stations, some hundreds of miles apart.
In the summary, he states that foliose lichens increase in dia-
meter from 0.3 to 3.5 cm. per year. Parmelia caperata (sterile),
measuring from 1.2 cm. across, reached in eight years 10 by 13 cm.
As far as I have been able to take measurements of increases,
they are as follows :—
Exact Measurements.
Parmelia physodes, on a fence, increased in one year from
0.9 to 2.0 cm. in diameter.
Parmelia physodes, on wortleberry increased in two years
2.0 cm.
Parmelia fuliginosa var. laetevirens, on elder, increased in
two years. 1.75 cm.
Approximate Measurements.
Parmelia saxatilis, on plane tree, 1 year, 2.7 cm.
Parmelia caperata, close to the sea, increased in two years
4.5 cm.
Ramalina calcicaris, on cone of Pinus Pinaster, in two years
had branches 3.1 cm. in length
6 Mycologia, ix., pp. 138-158 (1917).