and Genera 0/ ChlorospeiTiious Algae. 417 



A. Cells dividing by a simple dissepiment. 



Fam. 1. Palmelleae. 



The cells (like Protococcus) are laid without order, or in a qua- 

 ternary manner, in large numbers, within a common gelatinous 

 false frond. 



'' Cells free, or surrounded by a gelatinous mass, sometimes 

 stipitate ; propagation by the division of the endochrome, which 

 is mostly quaternary, and sometimes transformed into spores." 

 (Berkeley, p. 114.) 



In Ekeocapsa Hookeri, which is found in chalk-clefts in 

 Norfolk, "the inner membrane repeatedly bursts through the 

 outer, though always adherent behind, so as to form a gelatinous 

 mass of annulated threads, with a bright eye at the tip of each. 

 The endochrome is occasionally bipartite, and then each new 

 membrane acts for itself.^' (Berkeley, /. c. p. 117. f. 2S.) 



"The scattered cells in the early stages of Palmella are con- 

 nected by slender gelatinous threads radiating from a larger 

 central cell; the cells conjugate, two contiguous cells being 

 united by a narrow connecting tube, which soon enlarges, and 

 through which the contents of the two cells are mixed, and thus 

 a sporangium is formed, the membranes of the original cell 

 being absorbed." (Thwaites, Ann. Nat. Hist. ii. iii. n. s.) 



" In Palmoglcea Meneghinii, at least, there is a distinct coupling 

 of neighbouring spores; and Brebisson has noticed a similar 

 fact in Coccochloris protuberans and P. rubescens, while the trans- 

 parent peduncles point in the direction of certain Diatomaceae. 



"According as the endochrome divides vertically or transversely 

 the mass increases in width or length ; and as the diWsions alter- 

 nate after some tolerably fixed law, a network of greater or less 

 width is formed, according to the proportion of vertical and hori- 

 zontal division." (Berkeley, 119.) 



* Cells in a gelatinous mass. 



1. Palmella. 



** Cells in a confervoid simple or branched tubular Ji lament. 



2. Hormospora. {H. ramosa, Harvey, Ph. Brit. t. 213.) 



3. Hydrurus. [H. penicillatus.) 



B. Cells dividing by the formation of two new central half-cells. 



Fam. 2. Desmidiaceae. 



" Green ; the cells membranous, free from silex. Cells free, or 

 forming brittle threads or minute fronds ; increasing by the for- 

 mation of two half-cells in the centre or medial line, so that the 

 two new cells consist each of a new and old half-cell. Spores 



Ann. ^ May, N. Hist. Ser. 3. Vol. viii. 27 



