110 NOSTOCHINEiE. 



Order X.— NOSTOCHINEiE. 



N^ostochmece, Endl. ^rd Suppl. p. 12. Berk. Crypt. Bot. p. 139- J^ostochece, 

 Lindl. Veg. Kingd. p. 18. Kiitz. Phyc. Gen. p, 30. Nostochacece, Harv. Man. Ed. 2, 

 p. 230. 



Diagnosis. Green, fresh water, or rarely marine Algae, composed of moniliform 

 filaments, lying in a gelatinous matrix. Filaments formed of globose cells, here and 

 there interrupted by a single cell (heterocyst) of a difierent character. Propagation by 



zoospores. 



Natural Character. — The least organized plants of this Order consist of isolated, 

 moniliform threads, invested with a gelatinous coat, and either lying on the soil, 

 without a root attachment, or floating freely in water. Others a little more compound 

 are made up of numerous similar threads aggregated in bundles, and imbedded in a 

 gelatine common to the colony : while even the most complex, as in the genus Xostoc, 

 present but little further in advance, except that the gelatine in which the threads are 

 developed is of a firm consistence, when dry becoming quasi-membranous, and assumes 

 the character of a frond, with definite outline, but generally polymorphous shape. The 

 filaments are almost always simple, consisting of strings of cells, and are curved or 

 twisted, or often spiral ; in one case (Monormia) the filaments branch. The cells are 

 spherical or oval, never truly cylindrical with flat ends, as in the Confervacece, and are 

 filled with a dense, bright-green endochrome. In some few cases, as in Spermosira, 

 the moniliform thread is enclosed within a tubular, membranous sheath, as in Oscil- 

 latorice, and there is little to distinguish such plants from individuals of that Order, 

 except the occurrence of the cells called " heterocysts." These latter cells are destitute 

 ef endoclirome, but often clothed with cilia, and are of a difierent size and shape from 

 the neighbouring cells. They are always solitary, and occur at intervals in the fila- 

 ments, but vary in position in the difierent species. Their use has not been ascertained, 

 but they have been supposed to be connected with the male system of these plants. 

 They never change character, like the ordinary cells, and are always found occupying 

 a definite position in the filament, indicating that they perform some important function, 

 whatever it may be. 



Though the process of fertilization has not yet been observed, there can be little 

 doubt but that a true fructification is formed in the ordinary cells, which at first are 

 filled with pale-green matter, and afterwards increase in size, alter their form, and 

 acquire a much denser and more darkly coloured, often deep brown, endoclirome. All 

 the cells of the filaments do not exhibit tliese clianges, but only one or more, generally 



