322 Myxophycece 



The plants of this genus are most frequently met with in the British 

 Islands amongst Utricularia minor and submerged Sphagnum. The two 

 most widely distributed species are H. intricatus West (diam. of filaments 

 4 7 /x) and H. Hibernicus West & G. S. West (diam. of filaments 6 10 /j. ; 

 fig. 147). 



Family 2. SCYTONEMACE^. 



The plants of this family are at once distinguished from all 

 others of the Hormogonese by their type of branching. Except 

 in the three rare genera, Desmonema, Hydrocoryne and Diplocolon, 

 the cells are always disposed in a single series within a strong 

 tubular sheath of regular thickness. The trichomes of the 

 primary filament perforate the sheath at intervals and issue as 

 long flexuose branches, which develop a sheath of their own. 

 These false branches arise either singly or in pairs. The trichomes 

 are cylindrical, but towards the growing end of the filament they 

 increase in diameter, the cells becoming much shorter and more 

 rounded. The sheath may be homogeneous and colourless, or 

 lamellose and of a yellow or brown colour. 



The normal reproduction is by hormogones, but in most of the 

 genera ellipsoidal or globular spores are sometimes produced. 



The five British genera can be distinguished as follows : 



A. With one trichome in each sheath. 



* Filaments simple, un branched Microchcete. 



* Filaments with false branches (" pseudo-rami "). 



t Branches geminate, arising between the 



heterocysts Scytonema. 



tt Branches arising singly in the region of 



the heterocysts Tolypothrix. 



B. With 2 6 trichomes within each sheath. 



* Filaments straight, with basal heterocysts . . . Desmonema. 

 ** Filaments contorted within a common sheath Diplocolon. 



Genus Microchaete Thuret, 1875. [Coleospermum Kirchner, 

 1878.] The filaments are fixed at the base, erect, or tortuose- 

 flexuose, and without branches. The plants greatly resemble 

 unbranched species of Scytonema, and they occur in radiating 

 tufts or soft felt-like masses. Kirchner 1 has placed this genus 

 in the Nostocacese, but the presence of a prominent tough sheath 

 round each individual trichome, and the thick growing apices with 



1 Kirchner in Engler and Prantl's Natiirl. Pflanzenfam. i, 1 a, p. 76. 



