FLORWE/E 



217 



posdd, in its vegetative portion, of a single layer of cells ;: in bbtb" cases 

 coloured by phycoerythrin. >. The tetrasporanges ■ and the male and 

 female organs appear to be homologous to one another, and not to be 

 sharply differentiated. The tetraspores are motile for about forty-eight 

 hours after their escape from the tetrasporange ; by some writers they are 

 described as being endowed with an amoeboid change of form. , The 

 trichogyne is quite rudimentary ; 

 the pollinoixis attach themselves 

 singly or in niimbers to the fertile 

 portion of the thallus where the 

 ■oogonesi or- rudimentary carpogones 

 occur. While in this position they 

 are invested by a thin . cell-wall of 

 ■cellulose, and then put out a slender 

 thread of protoplasm which pierces 

 the. cell-wall of the oogone, nearly 

 the whole of the protoplasm of the 

 J)ollinoid passing into this organ. 

 According to Berthold, the contents 

 of the oogone break up, after impregnation, into eight carpospores, 

 the ' octospores ' of Janczewski, which move about, on escaping, in an 

 amoeboid manner^ putting out and withdrawing protoplasmic protru- 

 sion's, then come to rest, and germinate. Porphyra vulgaris (L.), not 

 uncommon on the coasts of Western Europe, is eaten under the name 

 * purple .laver.' 



Literature. 



Janczewski— Ann. Sc Nat., 1873, p. 241. 



Reinke — Pring-sheim's Jahrb. wiss. Bot. , 1878, p. 274, 



Goebel^Bot. Zeit.,-i878; p. 199. 



Berthold— Mittheii. Zool. Stat. Neapel, 1880 and 1882. 



Fic 195. — Tetraspores of B.angia fusco-purpic- 

 rea Lyng., showing amceBoid changes of form 

 (magnified). (After Reinke.) 



Thcjposition of the Ulvace^ is still uncertain. The group includes 

 a small number of genera— Ulva ((L.), 'Enteromorpha (Lk;), Phycoseris 

 (Ktz.), Prasiola (Ag.), ahd'i]Vr6nQstroma'(Thur.) — of fresh-water or more 

 often of marine or brackish Alg8e;"of'a bright green colour, consisting of 

 a fiat usually ribbon^shaped plate, feomposed of either one (Monostroma) 

 or two (Ulva) layers of cells ; less often (Enteromorpha) having the 

 form of a tube. This cells are sometimes arranged symmetrically in 

 groups of four (Prasiola). The male and female reproductive organs, 

 which are rudimentary in the Porphyracese, are entirely suppressed in 

 the.Ulvaceae,. and we find a reversion to a much simpler mode of repro- 



