NOSTOCEZ. 
B. Trichomes formed mostly of a 
single row of cells, Sheath slen- 
der. Aquatic plants ae like 
Tolypothria fs : 7 
(Sheaths enclosing several trichomes. F 
| Sheaths enclosing only a single trichome. 
Ramifications produced by the deviation of 
the trichome, which emerges from the side 
of thesheath . . : . . 
A. Ramifications usually geminate, pro- 
duced by a fold of the trichome 
which ruptures outside of the 
sheath, and gives birth to two 
filaments given off at a right 
angle. Heterocysts scattered 
here and there ‘in the trichome 
without any evident relation to 
the ramifications 
B Sheath very broad, forming 
a transparent layer around 
the trichome : . 
y Filaments agglutinated in 
erect wick-like bundles. 
B. Ramifications rarely geminate, often- 
times solitary, and originating at 
a point where the continuity of 
the trichome is interrupted by 
heterocysts. One or several he- 
terocysts placed directly above 
each branchlet . . 
Filaments agglutinated ag a 
more or jless firm mucilage. 
% Frond usually with a well de- 
12 CaLorRicHEx fined outline . 
Filaments free, growing in aust 
tufts, or forming a turf of 
considerable extent 
(Heterocysts scattered. Ramifications very 
irregular, arising from a fold in the tri- 
chome, in the form of a V, where originate 
two geminate filaments, distinct at the base, 
but at a certain height transformed, for the 
greater part, into a single filament, composed 
of a single row of cells. Frond hollow, but 
hard, folded and signage like a little Rivu- 
13 ¢ laria . 
Heterocysts tise Galasen at ‘the base of ie 
principal filaments and branchlets). Ramifi- 
cations produced by the transverse division 
of the trichomes, the upper part of which 
detaches itself and becomes a lateral branch- 
let, while the lower part extending itself by 
the side of its old tip makes a new extremity 
| similar to the first . : . . 
223 
. _ Haplosiphon. 
. 
Cystocoleus. 
Scytonema. 
Petalonema. 
Symphyosiphon. 
Tolypothria. 
. 18 
Calothria. 
Hormactis. 
. 14 
