264 NEMATOGEN^E. 



Plectonema Kirchneri, CooTce, Grevillea XL, p. 75. 



At first attached, but soon floating, and forming subglobose 

 woolly tufts, of a dark bluish green, changing to olivaceous. 

 Tufts from half an inch to an inch in diameter. Trichomes 

 radiating, with simple (rarely germinate) branches ; joints one 

 third or one fourth as long as broad. 



SIZE. Filaments '012-'015 mm. diam., with sheath. 



Plectonema mirabile, Kirch. Alg. Schles. p. 229 (scarcely of 

 Thuret). 



In ornamental water. Pleasure grounds, Kew. 



The filaments are much thinner than in P. mirabile and the branches 

 issue singly from the sheath, and not in pairs, as in that species. From 

 the dimensions given by Kirchner it seems probable that this is the 

 species to which he has given the name of P. mirabile. 



Plate CIV. fig. 2. a, tuft, natural size, b, trichomes X 400. 



FAMILY III. SCYTONEME^E. 



Filaments with lateral ramifications in which some of the 

 cells change into heterocysts. 



This family is divisible into two sections according to the direction 

 of the multiplication of the cells. 



: Cells only multiplying in the direction of the length of the filament. 



Scytonema, Petalonema, Symphyosiphon, Tolypothrix, 



Cystocoleus. 



** Cells multiplying as well in the direction of the breadth of the 

 filament, at least where the branches, which are always produced by 

 lateral multiplication, originate. 



Stigonema, Fischera, Haplosiphon. 



The last section includes many very doubtful forms, which will pro- 

 bably, as their development becomes better known, be transferred to 

 Lichens, of which they are presumably an imperfect condition. 



GENUS 107, SCYTONEMA. Ag. (1824.) 



Sheath enclosing a single trichome, ramifications produced 

 by the deviation of the trichome, which emerges from the side 

 of the sheath. Ramifications usually geminate, produced by a 

 fold of the trichome which ruptures outside of the sheath, and 

 gives origin to two filaments given off at a right angle. 

 Heterocysts scattered here and there in the trichome, without 

 any evident relation to the ramifications. 



