O e d e r i l N E M A T O G E N Æ .
Plants multicellular, or pseudo-multicellular. Cells forming
a filament (Trichome), usually included in a tubular homogenous
or lamellate sheath (vagina). Filaments (Trichomes) either
simple or branched.—Rabh. A lg . E u r. ii., 70.
Thuret unites CysUplim'oe and Sematogence in one order under the
name of Oryptophyoeat, representing the CystipTioræ by a Tribe called
Chrooeoccaceæ and Nematogenæ by another Tribe termed Nostochineoe, so
that really the difference is only one of name.
T e i b e 1. NOSTOCHINEÆ.
Trichomes simple or branched, with an obtuse, or acute and
setiform apex, either naked or enclosed in a sheath. Kepro-
duction by fragments of the triohome (hormogonia) which are
endowed with motion after separating from the mother plant
— Hormogoneoe. Thuret.
The Nostochineæ, as interpreted by Messrs. Bornet and Thuret, are
subdivided into two groups, or sub-tribes.
Sub-Tribe 1. P silonemæ with the filaments not attenuated at one extremity
to a hair-like thread.
Sub-Tribe 2. T e i c h o p h o e e æ with the apex of the filament attenuated
to a hair-like extremity.
Whilst the Chrooooooaceæ reproduce themselves by means of isolated
cells, the Nostoohineæ reproduce themselves by the fragments of filaments
(called hormogones), which are endowed with mobility after
separating themselves from the mother plant.
The filaments of Nostochineæ are composed essentially of coloured
cells disposed in a row. This assemblage of cells islspecially designated
a trichome. The trichome is either naked, or immersed in mucilage, or
enclosed in a sheath.
The presence or absence of heterocysts, their number, their situation
in the filament, are characters important to note, bnt which hitherto
have been much neglected. Easily recognized in the living plant by
tbeir yellow colour from the other cells of the trichome, but sometimes
difficult to distinguish in dried specimens. In doubtful cases it is to be
remembered that the heterooysts are united always with the sheath, and
if that envelope is defective in the other cells it will suffice to apply an
appropriate re-agent, snob as potass, solution of iodine, &o., to obtain
evidence of their nature.
Sometimes the terminal cells of the trichome resemble the others (as
in Lyngbya and Scytonema), sometimes the filaments are terminated by a
hyaline hair, elongated and deprived of its coloured contents, with a
diameter much less than the ordinary joints of the triohome (as Calo-
thrix, Rivularia, &o.). This distinotion, which corresponds in another
instance to the principal growing point of extension of the filaments, is
very marked in (he living state, and especially in individuals in full
vegetation. When, on the contrary, the plants are old, and the summit
broken and their hormogones dispersed, the complete filaments are
sometimes very rare, and must be sought with some perseverance.
Certain genera of Nostochineæ have the filaments constantly simple
(Nostoc, Anabaena), others have the filaments frequently provided with
lateral branches {àcytonemeæ, Calotricheæ). Sometimes these ramifications
are normal, and result from the regular division of the
triohome {Rivularia, &o.), sometimes accidental and irregular. These
produce themselves when the triohome has broken, they grow and issue
laterally from the sheath, when it is not rare to observe the base of the
filaments of certain Injnghya, or, again, when the hormogones are not able
to escape freely, they germinate in the interior of the sheath. Indeed,
it is very frequent that the germinations develope themselves in filaments
of all ages, but iu that case the young filaments are not at all
enveloped by the general sheath of the filament that bears them.
Nostocs should be dried as quickly as possible after they are collected,
otherwise the trichomes escape and the sheaths are left empty.—Thuret,
in Ann, des Soi. Nat. 6 ser., Vol. I., pp. 372-382 (1875).
The following is a dichotomous key to the classification as proposed by
M. Thuret:—
rFilaments tapering at the top into a hyaline
1 -s h a i r .................................................................
( Filaments always destitute of an apical hair .
rFilaments in which some of the cells change
2 1 into heterooysts ..............................................
V- Filaments without heterooysts
( Filaments with lateral ramifications
I Filaments without ramifications
/Filaments immersed in a gela-
\ tinons mucilage of a determi-
4 N ostoceæ < nate shape . . . .
y Filaments free or immersed in an
(. amorphous diffluent mucilage
Filaments consisting of a coloured triohome
enclosed in a hyaline sheath
Filaments without a sheath distinot from the
t r i o h o m e .......................................................
1. Heterocysts scattered in the trichome.
12
2
3
7
10
4
Nostoc.
. 5
. 6
A. B. C.
A. Spores originating in cells not adjoining
the heterooysts . . . .
/3 Trichomes united in small floating
bundles . . . .
Anabaena.
Aphanizomenon.
Sphxrozyga.
B. Spores originating in cells placed on
each side of the heterooysts
2. Heterocysts terminal {at both ends of the trichome).
C. Spores originating in cells placed just
below the heterooysts
f Cells disc-like. S p o re s v e ry p rom in e n t. He
6 ■< terocysts placed at regular intervals .
I Cells longer than broad. Spores none .
_ . ( F ilam e n ts sp ira lly tw is te d .
7 LYNGBVEiE I j'iiameiits not spirally twisted
Cylindrospermum.
jVodularia.
Microchcete.
Spirulina.
. 8