354 



On the Diatomacece. 



[Sess. 



Messrs Harvie-Brown and Buckley's ' Fauna of Argyll,' and is 

 the first capture, as far as I am aware, of the kind in the county. 

 In the immediate neighbourhood of Edinburgh, Daubenton's 

 bat has been caught at The Inch, near Liberton, by Mr 

 Speedy ; and this and other records of its occurrence will 

 be found in Evans's ' Mammalian Fauna of the Edinburgh 

 District.' 



IX.— ON THE DIATOM ACE JE. 



By Mr J. RUSSELL. 



(Read March 23, 1S9S.) 



The first point which will engage your attention will be the 

 answer to the question, What is a diatom ? In botanical 

 science the Diatomacea? form a sub- order of the natural order 

 Algae, and this sub-order is divided into two sub-sections — 

 (1) Diatomea?, microscopic plants with a siliceous epidermis; 

 and (2) Desmidieae, microscopic plants without a siliceous 

 epidermis. It is to the first of these sub -sections, the 

 Diatomese, that my remarks will be confined. 



The term diatom is given to the plant from its peculiar 

 mode of multiplying itself, the mother plant being, as it 

 were, cut through into two halves, each half forming a 

 complete plant in itself, and cut through in its turn, forming 

 again other two new plants. If we consider the diatom as a 

 unit, it is a one-celled plant of very small dimensions — how 

 small it is somewhat difficult for the mind to grasp'. Some of 

 the larger circular ones are about -ywG °^ an ^ ncn * n °^ a " 

 meter, while some of the smallest are less than ^ oo o °^ an 

 inch in diameter. I have called them plants because it is 

 now almost, if not altogether, universally recognised that they 

 belong to the vegetable kingdom : it was not always so, some 

 of the earlier workers considering some at least of the genera 

 as belonging to the animal kingdom. 



The term frustule is applied to the diatom as a unit. In 

 most, if not in all, species, the case — if the term may be allowed 

 — of this frustule consists of four distinct parts — two sides, 



