NOSTOCEA:, 225 
fragments of the trichome which he terms hormogones. The mucilage of 
old plants being softened, portions of the threads which lie between the 
heterocysts are detached and escape from the mucilage, whilst the hetero- 
cysts remain behind. These escaped fragments become endowed with 
motion, similar to that observed in Oscil/arta. The cells of the hormo- 
gone increase by division at right angles to the filament, and ultimately 
separate longitudinally, becoming the centres of new plants. 
Besides the reproduction by hormogones, certain special cells of the 
trichome enlarge and become converted into spores, which germinate and 
eats new plants, but no evidence of sexual reproduction has yet been 
adduced. 
Messrs Bornet and Thuret have subdivided the genus Wostoc into 
eight groups, of which two are not represented in Britain. The 
following is their synopsis, with the British species printed in small 
capitals. 
I, Intricata. Aquatic species. Fronds soft, gelatinous without deter- 
minate form, often floating. 
A. Trichomes forming irregular masses, de- 
prived of the general mucilage. 
Circumvolutions of trichome age and 
indistinct . ‘ - IL. hederule. 
Circumvolutions of trichome distinct ; . 2. tenuissimum. 
B. Trichomes involved in mucilage more or 
less abundant. 
u Trichomes flexuous, aggregated ; joints 
short and close together; sheaths un- 
coloured, very refractive . . 8. LINCKIA, 
B Trichomes loosely interwoven, pints 
of equal diameter, rather distant. 
1. Spores subglobose. ; . . 4, PISCINALE. 
2, Spores oval. 
* Mucilage soft; sheath none, 
indistinct, or uncoloured .» 5 CARNEUM. 
** Mucilage firm ; sheaths and 
mucilage tinged with yellow at 
the periphery . ‘ : . 6. revulare. 
II. GELATINOSA. Fronds soft and gelatinous; adherent; joints of 
trichomes cylindrically elongated in the young filaments, Spores 
oblong, large. 
A. Growing in watery or inundated places; 
fronds thick, deformed. 
a Trichomes heterogenous, composed of 
two sorts of joints, one cylindrical, the 
other cask-shaped or oe ea 
cal Ew . 7, SPONGIHFORME. 
B Trichomes iemeeandad : . 8. gelatinosum. 
B. Plant terrestrial. Frond plane, sepuited to 
the ground by the inferior surface % . 9, ELLIPSOSPORUM. 
III. Humirusa. Terrestrial species. Fronds at first globose, then con- 
fluent, and forming gelatinous cushions adhering to the substratum by 
their lower face, Spores smooth. 
A. Fronds in orbicular discs, or indefinite and 
continuous, 
