BRITISH DESMIDIE^. 189 



20. SCENEDESMUS, Meyen. 



Frond composed of two to ten fusiform or oblong cells, arranged side 

 by side in a single row, but after division in two alternating rows ; 

 division oblique. 



Cells always entire, and mostly fusiform or oblong, but in some 

 species the outer ones are lunulate. There is no constriction nor su- 

 ture at the middle, and the endochrome is not divided into two por- 

 tions by a transverse band. The cells are few in number, varying 

 from two to ten, and united into a frond by a hyaline matrix. Their 

 division is oblique, and not transverse, as in most genera of the 

 Desmidieaa. As all the cells divide simultaneously, the frond when 

 dividing consists of two rows, which are retained in connection by 

 the matrix for some time after the complete division of the cells. 

 From the oblique manner of division, the cells of one row alternate 

 with those of the other. 



The dividing frond is so unlike one having only a single row of 

 cells, that, in common with Meneghini and other naturalists, I formerly 

 considered these states as different species ; and it was only on seeing 

 a frond of Scenedesmus obtusus, in which the division of the cells was 

 still incomplete, that I discovered my error. The fact however was 

 previously known to Brebisson, and he has since sent me drawings 

 illustrating the process. 



The endochrome is in general very pale, and the starch granules 

 are inconspicuous. 



Scenedesmus differs from the preceding genera in the very different 

 form of its cells, but Pediastrum supplies a connecting link between 

 them. As in that genus, the frond in Scenedesmus is composed of 

 several cells, but these are differently arranged ; and the division into 

 two segments, which, although modified, is still met with in the 

 outer cells of Pediastrum, is entirely absent in Scenedesmus. In the 

 oblique manner in which its cells divide, it agrees with Spirotania, 

 which however has a different arrangement of the endochrome, and a 

 frond consisting merely of a single cell. 



