204 Chlorophycece 



processes. There are usually several parietal chloroplasts in each 

 cell, some or all of which contain a single pyrenoid. Multiplication 

 rarely occurs by cell-division as in Pleurococcus, but reproduction 

 commonly takes place as in that genus by the formation of non-motile 

 gonidia or spores. Zoogonidia are rarely developed and the plants 

 sometimes pass into a palmelloid condition (vide fig. 82 F). 



There are eight or nine British species of this genus, distinguished by their 

 external ornamentation. T. aspera (Reinsch) Hansg. (diam. veg. cells 13'5 29/* ; 

 fig. 82 A F), T. aciculifera (Lagerh.) Hansg. and T. reticularis (Reinsch) 

 Hansg. (diam. veg. cells 24 32 /* ; fig. 82 K) are amongst the most frequent 

 species met with in quiet waters. T. hirta (Reinsch) Hansg. (diam. veg. cells 

 17 27 /i; fig. 82 G and H) is often found on damp ground near the base of 

 tree-trunks. 



Genus Radiococcus Schmidle, 1902 1 . [Westella De Wild. 2 , 

 1897 (in part).] The plants consist of microscopic families of few 

 cells (generally four) arranged in a tetrahedral manner and 

 enveloped in a mass of jelly. The cells are rounded or occasionally 

 angular by mutual pressure, with firm cell-walls, and they contain 

 a single parietal chloroplast with one pyrenoid. Reproduction 

 takes place by the formation of four daughter-cells (spores) 

 tetrahedrally disposed within the wall of the mother-cell, which 

 ruptures and sets them free, the remains of the mother-cell-wall 

 persisting after the manner of Tetracoccus and Schizochlamys. 



The genus is distinguished from Tetracoccus by the smaller 

 families, which are enveloped in jelly, and by the tetrahedral 

 disposition of the cells. The plants often occur attached to the 

 under surfaces of water-lily leaves. 



There are two species of this genus 3 , of which R. nimbatus (De Wild.) 

 Schmidle ( = Pleurococcus nimbatus De Wild. ; Tetracoccus nimbatus Schmidle ; 

 Westella nimbatus De Wild.) is known from several parts of England. Diam. 

 of cells 8 15 p. In 1894 Schmidle 4 erroneously placed this Alga under 

 Ti'tracoccus and De Wildeman has further complicated matters by creating 

 the useless name Westella. 



Genus Protoderma Klitz., 1843 ; Borzi, 1895. This genus 

 occupies a position in the Pleurococcacese by reason of the resem- 

 blance between it and certain states of Pleurococcus vulgaris. The 

 plants generally consist of a minute thallus of short cell -filaments 

 radiating from a small central group of pseudoparenchymatous 



1 Schmidle in Allgem. Botan. Zeitschr. 1902, p. 41. 



2 De Wildeman in Bull, de 1'Herb. Boissier, 1897, p. 503. 



3 Schmidle in Hedwigia, 1902, Bd xli, Heft 4, p. 159. 



4 Schmidle in Flora, 1894, Heft 1, p. 45. 



