FLORIDE.-E 



217 



posed, in its vegetative portion, of a single layer of cells ; in both 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 pollinoids attach themselves 

 singly or in numbers to the fertile 

 portion of the thallus where the 

 oogones 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 

 pollinoid 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- 

 sions, 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 — Pringsheim's Jahrb. wiss. Bot. , 1878, p. 274. 



Goebel— Bot. Zeit. , 1878, p. 199. 



Berthold-Miitheil. Zool. Stat. Xeapel, 1880 and 1882. 



Fig 



195- 



Tetraspores of Bangia fusco-pjirpu- 

 rea Lyng., showing am'jeboid changes of form 

 (rDagnified). (After Reinke.) 



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

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

 (Ktz.), Prasiola (Ag.), and Mohostroma (Thur.) — of fresh-water or more 

 often of marine or brackish Alg^, of a bright green colour, consisting of 

 a flat usually ribbon-shaped plate, composed of either one (Monostroma) 

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

 form of a tube. The cells are sometimes arranged svmmetricallv in 

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

 which are rudimentary in the Porphyraceae, are entirely suppressed in 

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



