4 J8 PROTOPHYTA 



Botryococcus Ktz. consists of mulberry-like masses of thick-walled 

 cells united together into colonies, with no investing membrane, or only 

 a very slight one ; it is found in bog-pools, and is endowed with a 



rotating as well as a free-swimming 

 motion. It has possibly a genetic 

 affinity with the Coenobieae. 



In Urococcus Hass. the endo- 

 chrome is bright red, and the cell- 

 walls throw off successive layers of 

 FIG. w.-Botryo- ^^^^ mucilage, which form together a 



' FIG. 350. -Urococcus cylindrical or fusiform stalk, cora- 



P OSed > in SOme Species, of a large 



number of distinct annular segments. 

 Tetraspora Lk. is composed of cells associated together in large 

 numbers in a single layer imbedded in a copious gelatinous envelope. 

 It has no spontaneous motion, and is possibly allied to Merismopedia, 

 and also appears to have affinities with the Ulvaceae. Gay (Bull. Soc. Bot. 

 France, 1886, Sess. Extraord., p. 41) records in T. gelatinosa (Desv.) the 

 formation of biciliated zoospores, one being produced from the contents 

 of each cell, and afterwards becoming encysted into a resting-spore. 

 In Palmodictyon Ktz. the gelatinous envelope is filiform and branched, 

 and cell-division takes place chiefly in two directions only. 



The position of the following genera is very uncertain. Very 

 little is known of their mode of reproduction, and they lack the 

 copious gelatinous envelope which is characteristic of the family gene- 

 rally. They are mostly but feebly endowed with spontaneous move- 

 ments, and may probably be a resting 

 condition of algae or protophytes classed 

 under entirely different groups. 



Raphidium Ktz. includes several 

 species very common in fresh water, 

 and consisting of very narrow fusiform 

 acuminate cells, usually curved, solitary 

 FIG. 352. Scene- or joined together in bundles, the cells 



desmus obtusus , - . , , j i_ i 



Mey. (x 4 oo). being in the latter case united by their 

 (From nature ' ) middle, Cell-division takes place in one 



Ktz. (x 800). j- i 



(From nature.) direction Only. 



Under the class Palmellaceae are 



usually placed also the genera Scenedesmus Mey. and Polyedriuin 

 Nag., but their rank as independent organisms is exceedingly doubtful. 

 Their probable position has already been discussed under the heads of 

 the Sorastreae and the Pediastreae respectively (see pp. 303 and 299). 



