98 Chlorophycefc 



Order IV. SCHIZOGONIALES. 



The thallus is filamentous, sometimes (especially in young 

 stages) parenchymatous, and often expanded into broad sheets by 

 the fusion of the filaments in one plane. The cells are unirucleate 

 with a single central, stellate chloroplast, containing one pyrenoid. 



The plants are often attached by 'rhizoids' to a substratum, 

 and are subaerial in habit. 



The order is at once distinguished from the Chastophorales by 

 its chloroplasts, and by the division of the cells in two, and often in 

 three directions, especially in young plants. From the Ulvales it 

 is distinguished by its chloroplasts, by the more or less regular 

 longitudinal arrangement of the thallus-cells, and by the absence 

 of the vesicular stage in the growth of the young plants. The 

 plants of this order have most probably had a very different origin 

 from the Ulvales, the resemblance being only a parallelism of 

 modification. 



Family 1. PRASIOLACE^El. 



This family has been established to include those Alga 3 which 

 are embraced in the Schizogoniales. 



The thallus is commonly terrestrial, simple and filamentous, or / 

 forming flat, creeping expansions. It consists of a single layer of 

 cells produced largely by a fusion of the contiguous walls of cell- 

 filaments. Each cell possesses a central, stellate chloroplast with 

 one pyrenoid. 



Asexual reproduction takes place by gemmation and by the 

 formation of resting akinetes. Lagerheim has observed the pro- 

 duction of ' tetraspores.' 



Chodat regards the family as having analogies to the Bangiacese 

 among the Rhodophycere, both on account of the production of 

 tetraspores and the mode of growth. 



Genus Prasiola Ag., 1821. [Indus. ScJiizogoiiiam Klitz. 1843, 

 and Hortniditim Kiitz. 1843.] The genus occurs on moist earth, 

 rocks, stones, old walls, trunks of trees, etc. The thallus is 

 filamentous, consisting of one, two, or many series of cells, or 

 foliaceous and expanded with the cells arranged more or less in 

 groups of four. The cells of the ordinary filaments are broader 

 than long and those of the flat expansions are quadrate or polygonal 



