Mcbeeira.] ALG1E, DIATOMACEjE. 249 



Div. IV. DIATOMACE^E.* 



Granules (frustula) of various forms, plane or compressed, 

 more or less hyaline or transparent, rigid and fragile, in parallel 

 series or circles, free, naked, or imbedded in a mucous mass or 

 gelatinous frond, at length separating into definite segments. 

 Small, often very minute plants, in the sea or in fresh water, 

 mostly parasitic, or forming floating masses, or mixed with other 

 aquatic vegetables. Grev. 



TRIBE XXII. DESMIDIE^. 



Filaments cylindrical or angular, at length separating into 

 segments (frustula.) Grev. 



89. MELOSEIRA. Ag. Meloseira. 



Frustula forming simple, pseudo-articulated filaments, con- 

 stricted at the articulations, fragile, easily separating. Grev. 

 Name ; pe\os, a membrane, and ecipa, a chain; in reference 

 to the form of the filaments. 



1. M. lineata, Ag. Striated Meloseira. Filaments fragile, 

 contracted at the articulations, transversely striated with one 

 or two fine lines, the joints 2 3 times longer than they are 

 broad. Grev. Grev. in Hook. Br. Fl. v. ii. p. 4Q2.Conf. li- 

 neata, Dillw. p. 44. t. B. 



In streams and ditches, floating in dark-brown masses. At Plassey, 

 near Limerick ; W. H. Harvey. The Endochrome, a brown colouring 

 matter of the joint, becomes finally parted into two distinct masses of 

 a roundish oblong figure. 



TRIBE XXIII. FRAGILARIE^E. 



Filaments plane, extremely fragile, composed of rectilinear frus- 

 tula. (Frustula sometimes apparently radiating from a centre, 

 and not presenting the appearance of a filament.) Grev. 



9 Irish Botanists have scarcely attended to this minute but curious tribe of 

 Plants, (we have yet had no Carmichael or Greville amongst us) ; and I am 

 ashamed to say, that out of fifty-seven British species most, if not all, of 

 which are probably natives of Ireland I can only claim eighteen as having a 

 right to a place in our Flora. Of the following British genera no species has 

 hitherto been noticed in our rivers, or on our shores : Desmidium, Achnanthes, 

 Styllaria, Homceocladia, JBerkeleya, Micromega, and Cymbella. Not being 

 very conversant with these plants, I have, in the following descriptions, adhered 

 to Dr. Greville's words in Hook. Brit. Flora, vol. ii. p. 401, tt seq. 



2 H 



