230 NOSTOCHACE^. 



2. S. Hutchinsia, Kiitz.; ''marine, aeruginous, aggregated ; 

 spirals very dense, distinct." Kiitz. 

 Shirehampton, Mr. Thwaites. 



Order XVIII. NOSTOCHACE.^. 



NosTOCHiN.E, Harv. Man. ed. 1, p. 13. Nostochine.e, 

 Eiidl. Sd Suppl. p. 12. NosTOCHE^, Lindl. Vey. King. p. 

 18. Kiltz. Phyc. Gen. p. 30. (Part of Nostochince, Ay. and 

 other authors. J 



Diagnosis. — Green, fresh-water, or rarely marine. Algae, 

 composed of moniliform filaments, lying in a gelatinous 

 matrix. 



Natural Character. — Plants sometimes furnished with 

 firmly gelatinous, but never truly membranaceous, fronds of 

 definite outline, variously lobed or extending into sub-regular 

 branches; sometimes mere masses of jelly or slime, through 

 which filiform strings of cells are dispersed. Cells spherical 

 or oval, filled with bright green endochrome, linked toge- 

 ther, end to end, into moniliform filaments, which are some- 

 times simple, sometimes, but rarely, branched, and are almost 

 always curved or twisted, often taking a spiral direction. In 

 the higher examples of the order a multitude of such threads 

 is contained within a firm jelly, through every part of which 

 they are dispersed ; but in the lower members the filaments 

 are separated, or lie in an indefinite slimy substance. The 

 cells composing the filaments are of two kinds ; first, the 

 bright green ones already described, which constitute the 

 greater part of the filaments ; secondly, solitary cells of dif- 

 ferent form and size to the rest, destitute of endochrome, and 

 often clothed with cilia. These cells occur at intervals in all 

 the filaments, but vary in position, being sometimes found at 

 one end of the filament, sometimes in the centre. They are 

 called " connecting-cells" or " heterocysts." Their use is 

 unexplained, unless they be representatives of the male sys- 

 tem in these plants. This would seem probable by their 

 never altering their character, while fructification is constantly 

 formed in the other cells. The regularity of their occur- 



