214 ALG^ 



Batrachospermum, more or less imbedded in the thallus in the other 

 genera of the order. In several of the genera tetraspores are unknown. 

 A very singular genetic connection exists between the genera Chan- 

 transia and Batrachospermum, it being possible to transform the former 

 into the latter by changing its conditions of life. The germinating 

 carpospores of Batrachospermum put out a kind of protoneme, which is 

 the Chantransia of Fries, the non-sexual generation of Batrachospermum ; 

 this can propagate itself by simple budding from generation to genera- 

 tion, producing, as a rule, as its organs of propagation, only non-sexual 

 tetraspores. Chantransia grows especially in dark situations under water, 

 and, when transferred to the light, undergoes a metamorphosis. There 

 springs up from the Chantransia protoneme a branch which is in every 

 respect a Batrachospermum, and which bears sexual organs only, and 

 no tetraspores. On one species only of Chantransia, C. corymbifera 

 (Thur.), are sexual organs known. Although this phenomenon is some- 

 times spoken of as an example of ' alternation of generations,' it is not 

 identical with the process known under that name in the higher Crypto- 

 gams, being rather a difference in the mode of development dependent 

 on a change in the vital conditions. 



Literature. 



Solms-Laubach— Bot. Zeit., 1867, p. 161. 



Sirodot — Compt. Rend., Ixxvi., 1873, pp. 1216, 133S ; Ixxix., 1874, p. 1366; xci., 



1880, p. 862 ; xcii., 1881, p. 993 ; Bull. Soc. Bot. France, 1875, p. 128 ; and 



Les Batrachosperm&s, 1884. 

 Aicangeli — Nuov, Giorn. Bot. Ital., 1882, p. 155. 

 Massee — Journ. R. Microsc. Soc, 1886, p. 561. 



The LEMANEACEiE are a small group of fresh- water Algse, comprising 

 the genera Lemanea (Bory) and Sacheria (Sir.), growing in rapidly running 

 water, as beneath mill-wheels. The thallus is filiform and cartilaginous, 

 of a dull grey or greenish colour, and consists of a single row of tubular 

 cells, or of an axial row surrounded by rows of smaller cortical cells ; it 

 displays swellings or projections at regular intervals. It grows by means 

 of an apical cell, from which segments are cut off at right angles to the 

 direction of growth. By transverse septation each segment divides into 

 a central Cell surrounded by peripheral cells ; the central cell becomes 

 a member of the central axis, the peripheral cells members of the cortical 

 tubes. The ' frond ' increases by budding at the free surface of the 

 rooting system, finally producing caespitose tufts. No non-sexual spores 

 are known. The only other mode of reproduction is sexual. The 

 antherids are short cylindrical cells produced externally in the neigh- 



