f
il
■1
I
ill th Spores originating e lower p a rt of the
trichome
Trichomes never producing any spores .
A. Frond having a tendency to an
hemispherical or bladdery form.
Filaments exhibiting a disposition
to radiate from the base of the
frond . . . . . .
Filaments erect,
Glceotriclia.
. A.
/3 Frond flat,
parallel
llivul(XYÍa.
. Isactis.
Sah~tribe I. P s il o n em eæ , Filaments not attenuated into a
hair-like extremity.
F a m i ly I. NOSTOCEÆ.
Trichomes furnished with lieterocysts, involved in a very
copious gelatin, more or less firm or diffluent, which is collected
into a variously expanded, or very often indefinite thallns, or
rarely with the mucilage quickly dissolved, subsolitary.— Borzi
Alg. Fico. p. 279.
Gbnus 94. NOSTOC. Vauch. (1803.)
Thallus gelatinous or membranaceous, g irt by a more or less
firm periderm, definite, globose, or variously expanded. Trichomes
flexnously curved, irregularly interlaced, now and then
vaginate, joints globose or elliptical, distinct, or more or less
closely connected. Heterooysts terminal or intercalated, larger
or equal to the other cells. Spores equal to the heterooysts, or
a little larger, green, becoming bluish, olivaceous, or yellowish
brown.
The Nostocs consist of a more or less firm jelly, in which headed filaments
are imbedded, consisting of chains of small, somewhat globose
simple cells. These filaments or trichomes are usually surrounded by a
.sheath, which is often so delicate as scarcely to be visible, or it is almost
obsolete. The frond or thallus may be globose, discoid, lobed, or
irregular, with a more or less distinot outer layer forming a kind of
epidermis.
At irregular distances in the trichomes are larger cells, or heterooysts,
formerly regarded as spermatia, which differ in colour from /h e other
cells of the trichome. Individual cells become heterocysts uninfluenced
by any definite law at present demonstrated.
Increase in the filaments is caused by division of the cells in the longitudinal
direction, whereby the triohome is constantly being lengthened,
and new cells added, which lie in the mucilage.
Thuret has explained the process by which new plants originate from
fragments of the trichome which
old olants being softened, portions of the threads which I
Separate longitudinally, becoming the centres of new plants.
Resides the reproduction bv hormogones, certain special cells of the
tricho ne e, large and become ¿onverted into spores, which S®™’«® ®
p ro d re new pfauts, but no evidence of sexual reproduction has yet been
adduced.
Messrs Bornet and Thuret have subdivided the genus AWoe into
eic/ht groups, of which two are not represented in B itain. The
following is their synopsis, with the British species printed in small
capitals.
T I n t m CATA. Aquatic species.' F ro n d s soft, gelatinous without deter-
minate form, often floating.
A Trichomes forming irregular masses, de-
prived of the general mucilage.
Circumvolutions of triohome compact and
in d is tin c t. . •
Circumvolutions of trichome d is tin c t.
B. Trichomes involved in mucilage more or
less abundant.
a Trichomes flexuous, aggregated ; joints
short and close together; sheaths un.
coloured, very refractive
j3 Trichomes loosely interwoven, joints
of equal diameter, rather distant.
1. Spores subglobose.
2. Spores oval.
* Mucilage soft; sheath none,
indistinct, or uuooloured .
** Mucilage firm ; sheaths and
mucilage tinged with yellow at
the periphery . . . .
1 -
2. tenuissimum.
3. 1INCKIA.
4. riSCINALE.
5. CARNEUM.
6. rivulare.
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 compressed spheric
a l .............................................■ '
p Trichomes homogenous
B Plant terrestrial. Frond plane, applied to
the ground by the inferior surface
tbeir lower face. Spores smooth. _
A. Fronds in orbicular discs, or indefinite and
continuous.
7. SPONGIÆFOBME.
9. e l l ip s o s p o e u m .