138 [Proc. B. N. F. C, 



water. These are the microscopic plants known as fresh water 

 Algce. They are formed everywhere where water collects in 

 large or small quantities — in lake, river, pond, canal, or ditch, 

 as well as in the tiniest tricklet by the wayside path, and even 

 on the face of damp walls and slippery surfaces of mountain 

 rocks. One great family of these Algce is the Diatoms, which 

 are aquatic plants, consisting of a single cell, the colouring 

 matter of which is uniformly of a pale golden brown when 

 living. Their peculiar characteristic is their skeleton, which 

 is a pair of plates of indestructible silex, and when the plant 

 dies the tiny frame remains, so that in some places they form 

 immense beds many feet thick composed of myriads of Dia- 

 toms. The Desmids are another group of single-celled Algce. 

 They consist of a transparent envelope enclosing a bright green 

 colouring matter, the forms and arrangement of which are very 

 varied, and form the basis of the genera and species into which 

 they are divided. Besides these two, there is another great 

 tribe of fresh-water Algce, including very different forms, some 

 of which, in their thread-like fronds, much resemble their 

 relatives of the sea, while others grow on damp soils and clays, 

 or swim freely, or even spin round in the water. One species, 

 which grows in pools, often spreads over the entire surface of the 

 water, and can be lifted out and dried, when the thick felted mass 

 is not unlike a blanket of faded green baize. Of these a fair 

 number have been recorded as occuring in the North of Ireland, 

 from gatherings made during recent botanical excursions, in all, 

 so far, three hundred and eight species : but this is very far 

 short of what might be found in the district if observers would 

 collect, examine, and name their finds. This, it is to be hoped, 

 will be done, so as to enable a list of all the fresh-water Algce 

 occuring in the North of Ireland to be published by the Club, 

 and thus fill a long-standing gap in the natural history of the 

 neighbourhood. The work is one in which all possessed of 

 a microscope can participate, as the material requires no tedious 

 preparation before examination, but can be put on a glass slip 

 on the stage, just as it is taken from the water; and, moreover, 



