4)8 



PROTOPHYTA 



Fig. 349. — Boiryo- 

 coccus Braunii 

 Kt2. ( X 400). 



Fig. 350. — Urococcits 

 instgnis Hass. ( x 

 400). (From nature.) 



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 Coenobiese. 



In Urococcus Hass. the endo- 

 chrome is bright red, and the cell- 

 walls throw off successive layers of 

 mucilage, which form together a 

 cylindrical or fusiform stalk, com- 

 posed, 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 algse 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 

 or joined together in bundles, the cells 

 being in the latter case united by their 

 middle, Cell-division takes place in one 

 direction only. 



Under the class Palmellaceae are 

 usually placed also the genera Scenedesmus Mey. and Polyedriiim 

 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). • 



Fig. zS'^.— Raphi- 

 dium yalcaUitn 

 Ktz. (x 800). 

 (From nature.) 



>/f 



Fig. 352. — Scene- 

 desmtts obt-usus 

 Mey. ( X 400). 

 (From nature.) 



