258 ALG^E 



Cornu (Chromophyton) Bull. Soc. Bot. France, 1883, p. xciii. 

 Hansgirg Oesterr. Bot. Zeitschr. , 1884, p. 31. 

 Lagerheim Ber. Deutsch. Bot. Gesell. , 1888, p. 73. 



Phceothamnion Lagerh. (Bot. Zeit., 1885, p. 604) is a fresh-water 

 alga forming brownish yellow tufts on Vaucheria, Cladophora, &c. 

 Certain cells develop into zoosporanges, each of which produces two 

 biciliated zoospores, and the alga has also a palmella condition. Not- 

 withstanding the brown endochrome, and the fact that the zoospores 

 germinate directly and have not been observed to conjugate, Lagerheim 

 places this genus near to Chroolepideae and Chsetophoraceae, making it 

 the type of a new family; PH^EOTHAMNIE^:. It may possibly, however, 

 be more nearly related to the Syngeneticae. 



Class XIV.- Conjugate. 



The Conjugate, as defined by de Bary, constitute an extremely well- 

 marked and natural group, composed of the three families Mesocarpacea, 

 Zygnemacea, and Desmidiacetz, with no near affinities (except possibly 

 with the Diatomaceae). The. individual is unicellular in most of the 

 Desmidiaceae ; but in some genera of desmids, and in all belonging to 

 the other two orders, it consists of a filament of cells, which is almost 

 invariably unbranched. The arrangement of the bright green endo- 

 chrome, in spiral bands, plates, discs, or stars of beautiful symmetry, is 

 altogether peculiar to this group of plants, and renders them among the 

 most interesting and beautiful of microscopic objects. No formation 

 of zoospores occurs throughout the class, and the ordinary mode of 

 vegetative increase is by simple cell-division, and the breaking up of old 

 individuals in the filiform genera into fragments. They retain their 

 power of life through the winter, when under conditions unfavourable to 

 the formation of zygosperms, by the production of resting-spores, or 

 single cells which retain for a long period their vitality. These may be 

 either akinetes or aplanospores in Wille's sense of the terms. Gay states 

 (Bull. Soc. Bot. France, 1886, p. 41) that the filaments of Zygnema 

 (Ktz.), especially when growing in dry situations, have a tendency to 

 break up into cysts, i.e. fragments which become enclosed in a mucila- 

 ginous sheath, resulting from the gelifi cation of the outer layers of the 

 cell-wall. These cysts may preserve their vitality for months, and 

 then, when moisture again penetrates the sheath, they divide by trans- 

 verse septa, and develop into new individuals. The single cell of the 

 Desmidiaceae and the filament of the filiform genera is enveloped in a 



