i i
I
.G
■ U
1 1
F a m i ly IV. PITHOPHORAOEÆ.
Chlorophylliferous Cladopliora-like Fresk-water Algæ, consisting
of cells formed by bipartition of tbe terminal cell, tbe
thallus having two distinot p a rts—(1) the oauloid part,
developed from the germinated spore upwards, propagative, and
almost always branched, tbe branches placed a little space
below the top of tbeir supporting cells ; (2) the rhizoid part
developed from tbe germinated spore downwards, almost always
sterile and branchless, commonly unioellular. Spores neutral,
quiescent (agamo-hypnospores), generally cask-shaped, single,
formed by division into two of the cauloid cells, of the chlorophyll
filled, and commonly widened upper parts of these cells ;
in germinating, as a rule, dividing into two cells, the one
giving rise to the canloid and the other to the rhizoid part
of the thallus.— Wittrock, Monograph o f the Pithophoracece,
p. 46,
For full details of this Family, consult Prof. V. B. Wittrock “ On the
Development and Systematic Arrangement of the Pithophoraoeæ ” (published
in English). Upsal, 18T7.
Genus 63. FITHOFHOB .A. WiUr. (1877.)
Character the same as th a t of the family given above.
The formation of spores is effected iu the following manner The
Upper part, of the mother cell of the spore, is somewhat widened.
The ohlorophyll-coloured protoplasm in the lower, not widened, part of
the cell then passes little by little into the upper and widened part, till it
is quite filled with chlorophyll-coloured protoplasm. A transversal cell
wall is then little by little formed just below the point where the
widened part of the cell commences. In this manner are formed one
lower cell containing but little protoplasm, almost devoid of chlorophyll,
the so-called aubsporal cell, and one upper cell, rich in chlorophyll and
reproductive, the spore. Its shape is, as a rule, cask-like or oylindri-
cally cask-like. When the membrane of the spore has attained a not
inconsiderable increase iu thickness the spore reposes some time before
germinating, and consequently belongs to the class of spores which is
called hypnospores, ^ With regard to its origin, it may be called an
agamo-spore, as being formed neutrally without any fecundation.
Formation of spores may take place in all the cells of the oauloid, in the
terminal as well as in the inclosed. As a rule it begins in tbe youngest,
i.e., the terminal cells ; afterwards proceeding downwards, or, in other
words, basipetally, in the principal filament as well as in the branches.
I t is these spores which give origin by their germination to the course of
development already described. In this manner you will see one neutral
generation, forming hypnospores, follow upon another, in an uninterrupted
series, without any metagenesis.
PITHOPHORAOEÆ. 147
The reproduction of individuals may, however, be effected also in another
way than by the formation of spores. Besides the specimens which
form spores, there are others which never do so. These, which are distinguished
by a richer ramification, transform part of their cells iuto so-
called “ prolific cells.” A common vegetative cell grows richer in
chlorophyll coloured protoplasm and starch, and is thus made fit to form
a new individual. This the prolific cells do, when they have been made
free, by the destruction of the mother specimen, by forming a new specimen
laterally near their top, iu the same manner as a branch—and later
a system of branches—is formed by a cell in the fertile specimens. That
the specimens originated by prolific cells have the power of forming
spores is certain, as well as that specimens forming prolific cells may
have been originated by spores. I do not know with certainty whether
specimens forming prolific cells may have been originated by prolific
cells themselves, but it seems to me in no wise improbable.—
rock, 1. c.
F ith o p h o ia K ew e n s is .— Wittr. Mon. p. 52.
Principal filament of the cauloid p a rt of the thallus, in fertile
specimens, on an average -059 m. thick, with solitary branches
of only one degree (rarely of two), spores single, partly enclosed,
partly terminal, the enclosed spores cask-shaped, but more
elongated, on an average -08 m. thick and -2 m. long, the
terminal spores cask-shaped, with the upper end conical and the
top somewhat rounded, on an average ’088 mm. thick and '219
mm. lo n g ; the rhizoid p a rt of the thallus as a rule unioellular.
W ittr. Mon. Pithoph. t. 1 f. 8, t. 2 f. 1-12; t. 3 f. 1 -9 ;
t. 4 f. 2-11 ; t. 5 f. 9 10.
In tank. Water-lily house, Kew Gardens. August.
This singular plant is thought by Wittrock to have been an importation
from Brazil. It has not been seen in its original locality for two or
three years.
Plate LVI, fig . 8. Portion of spore-bearing filament x 20. Fig. 9,
portion of principal filament with spore forme(3 at the apex of a short
branch, and another in process of formation in the principal filament
X 200. Fig. 10, a mature enclosed spore x 200. Fig. 11, part of cell
from rooting portion of a sterile thread x 200. All after Wittrock.
■
ii
I ll
i: i