Asplenium lanceolatum on the Coast of WicklowAuthor(s): John A. J. PalmerSource: The Irish Naturalists' Journal, Vol. 2, No. 6 (Nov., 1928), p. 120Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25531588 .

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l'iO The Irish Naturalists' Journal, [Vol. it.

ASPLENIUM LANCEOLATUM ON THE COAST OF WICKLOW. While on holidays in the Arklow district, during the first two weeks in

July, I found a fern on the cliffs near Arklow Head which was unfamiliar. Miss Knowles, of the National Museum, Dublin, has identified it as

Afiplcnium lanceolatum Huds., and states the plant appears to..resemble

specimens in, the National Herbarium from the coast of Cornwall rather than those from the known Irish stations. JOHN A. J. PALMER.

18 Waterloo Road, Dublin.

LYCOPODIUM INUNDATUM IN WICKLOW. On the 20th June last, while strolling along the south shore of the Lower

Lake of Glendalough, I found some small pieces of an unfamiliar

Lycopodium, and on taking it to the National Museum for comparison came to the conclusion that it could only be L. inundatum. I revisited the spot three weeks later with Mr. M. J. Gorman, arid we were able to trace it for about sixty yards along the swampy ground at the S.W. corner of the

lake, close to the water's edge. This is a remarkable extension of its Irish

range, as it has hitherto only been recorded from' West Cork, Kerry, Coimemara, Achill arid lnishbonn. J. P. BRUNKER.

18 Grosvenor Place, Rathgar, Dublin.

FRESHWATER AhOM AND THE PURIFICATION OF WATER SUPPLIES.

By Mabel Clapiiam, B.Sc.

The green algae or green "seaweeds'* which live in fresh water

play an important part in the nitration of water, and the bene ficial effect of slow sand filtration is due mainly to them.

A sand filter consists of a watertight tank with successive

layers of fine sand, coarse sand, pebbles, a fine gravel and lowest

of all, a large gravel, theseiayers being some 4?5 feet deep in all.

In the lowest gravel layer, brick channels are placed to carry off

the filtered water which percolates through the sand layers. Water enters the filter by a channel above the level of the sand,

and is allowed to flood the tank gently to a depth of about 4 or 5 feet.

For the first few days (depending on the weather and time of year) the water passing through the filter is merely mechanically strained, and bacteria, being smaller than the spaces between the

sand particles, easily pass through. This water is allowed to run

to waste. After this time a film is formed on the surface of the sand. Animals such as Amoeba, Arcella, and certain of the In

fusoria, and colloidal material present in the raw water may be

found in the film, but it is composed chiefly of algae. At Bally sallagh this film has been found to consist of such comparatively large forms as Chactomorpha, Sphacroplca, Hormospora, Mou

gcotia, Spirogyra. These form a network on the surface of the

sand, the meshes of which are filled in by diatoms, unicellular

algae and zoogloea of bacteria, whose gelatinous envelopes hold

them together and cause them to adhere firmly to the sand

particles. These algae are alive, and grow under such conditions.

Carbon dioxide is supplied by the water filtering through, and in sheltered corners the bacteria break down organic material, thus

producing nitrogenous compounds assimilable by the algie. The

active photosynthesis carried on by the "seaweeds'* liberates

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