Mr. Thompson on an Alga which colours Bally drain Lake, 75 



phanea by Hampe are characterized, just as in the Sphar/necp, 

 by peculiarities in the structure of the leaf, which consists of 

 two dift'erent species of cells, some narrow and filled with 

 chlorophyll, others wider, transparent, and perforated with 

 pores which afterwards pass into holes. The diflferences de- 

 pend, with the exception of the structure of the sides of the 

 cells, particularly upon the arrangement of these two species 

 of cells. In SphaffnecE both lie more or less in one plane, and 

 so form but one layer, of which the whole leaf consists ; in 

 LeucopJianeee the green cells are always covered on both sides 

 with 1, 2, or 3 layers of the large transparent perforated cells. 

 From this arrangement, by which the green cells are greatly 

 obscured, results that glaucous colour which characterizes the 

 whole tribe at first sight, together with its peculiar quickly 

 drying and brittle as well as moist and flexible habits. 



X. — On a minute Alga which colours Bally drain Lake, in the 

 county of Antrim. By Wm. Thompson, Esq., Vice-Pres. 

 Nat. Hist. Society of Belfast. 



July 25, 1838. — Late in the autumn of 1837 I observed 

 patches of a singular looking blueish green scum at the edge 

 of Ballydrain Lake — a beautiful and picturesque sheet of water 

 situated a few miles from Belfast* — but being hurried at the 

 time, I did not procure specimens for examination. This I 

 had intended to do a few days afterwards, but circumstances 

 prevented its accomplishment at that time, and when I soon 

 afterwards returned the plant had disappeared. On visiting 



* Ballydrain Lake covers about twenty acres of a sandy and peaty soil, and 

 its elevation above the sea is perhaps forty feet. It is of various depth, is 

 fed by springs, and has an outlet in but one small brook. During winter it 

 is the daily haunt of great numbers of wild fowl {AnatidcB) of various spe- 

 cies, that resort to it as a secure asylum ; and 1 am happy to say not in vain, 

 for agreeably to the good taste of its proprietors, a shot is not permitted to 

 be fired upon it ; but, notwithstanding, these most attractive birds have been 

 on the decrease for the last few years. In fishes, mollusca, or other plants 

 than those here treated of (unless more microscopic species remain to be dis- 

 covered), it possesses no peculiarities. MyriophyUum, buck-bean {Meiiy- 

 anthes), and the larger phenogamic plants generally, have much increased of 

 late years, to the detriment of pike-fishing, the vegetation near the edges 

 being so dense as to couceal the bait placed on night lines for tlie capture of 

 these fish. 



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