The following is a snmmary of Eostafinski and Woronin’s researches
on this genus :—
If a plant be placed in water, its contents become modified at the
latter part of the day or a t night into zoospores. Ultimately the wall
swells, then bursts somewhere at the top, and the zoospores resulting
from the division of the parietal stratum escape. If the plant be only
moistened, the zoospores do not swarm out, but come to rest within the
collapsed wall. Such were known to previous observers as “ germ
cells ” or “ gonidia.”
The zoospores are elongate-oviform, 5-8 X 20 mm., with a single
flagellnm, and 2 to 4 chlorophyll granules. Having swarmed out, they
soon come to rest, lose the flagellnm, become surrounded by a membrane,
increase in size, and germinate on damp earth, in which stage
they represent the so-called Protococcus botryoides.
The large ordinary zoosporangia are also otherwise modified. If one
is allowed to dry, its membrane collapses, loses colour, and soon becomes
empty. The protoplasmic contents pass down to the ramifications of
the root. Here they break np into numerous cells, sometimes two or
three side by side, but chiefly in a continuous chain ; each cell furnished
with a separate membrane.
These are capable of three forms of development :—(]) If removed
from the soil and placed in water, the cell becomes a subterranean
zoosporangium. The formation of the zoospores is independent of light
at any hour of the day or night. The zoospores are similar to those
above described, and germinate in the same manner. (2) If a chain of
these root cells be laid on moist earth, each protrudes a hyaline process,
which enters the soil, the opposite end being elevated, and thus each
root cell becomes a vegetative plant. (3) If the root cells are not
removed, and kept equably moist, they also germinate in the earth,
become inflated, put forth a root process, the wall of which becomes
very much thickened on the inner side below the inflated upper portion.
By intercnlary growth of the root portion the upper part becomes raised
aloft, so that the apex is carried above the surface of the soil. These
products of modified root cells are named hypnosporanges, and are equivalent
to so-called Botrydium Wallrothii. When dried, the hypno-
sporanges retain their power of germination during the whole year, and
when placed in water ^ form zoospores at any hour of the day and night,
germinating and forming yonng plants as above,
The nniflageilate zoospores germinate on a moist substratum. On
earth or sand they thrive badly, but better on clayey or muddy soil. In
water they never germinate, but come to rest, are surrounded by a
double membrane, and lie dormant for months. If these be transferred
upon a clayey soil, they commence to form a vegetative plant. If the
zoospores be sparingly distributed over the soil, and the whole kept
equally moist, the vegetative plants become ordinary zoosporanges. The
plants are sometimes modified into hypnosporanges.
Thus, vegetative plants can be increased by cell division directly
from zoospores, become ordinary zoosporanges, with such consequences
as root cells, &o., or they may be directly modified into hypno-
sporanges. But there is yet another way in which existence may be
carried on. If exposed to drought, the following phenomena occur ;_
The wall collapses more or less, and the protoplasmic contents break up
into a number of cells, each surrounded by a delicate membrane, its
■contents homogeneous, at first green, then passing into red. These are
the spores, and have been known by such names as Protococcus coccoma,
P. palustris and P. botryoides. These spores become changed in water
to zoosporangia, their contents giving rise to zoospores in the manner
already desorihed. If the spores be still green, their zoospores will
have a distinot fusiform figure, with two cilia at one end. They consist
of slightly coloured protoplasm. These zoospores conjugate in twos,
sometimes several together. They come in contact by their ciliated
ends, then come to touch laterally by the uuooloured portions, when
the fusion of the conjugating zoospores takes place, immediately after
which they present a cordate figure, and in the middle a colourless
vacuole, Finally, the isospore thus origiuating becomes globular, the
vacuole occupying the centre.
If the zoospores be isolated before conjugation, they will in the end
break np, without presenting any products capable of germination.
The zoospores originating from red spores have a different figure,
their posterior end being rounded, but they have otherwise the same
structure, and behave in the same manner as the others. The red
spores maintain their germinative power for years, but after two years
their zoospores are languid, and offer a parthenogenesis of a peculiar
kind. The red spores, if kept moist only, become nothing altered after
weeks, whilst the green, under these cironmstauoes, may directly
germinate into vegetative plants.
The isospores are at first globular, and capable of immediate germination.
They also present resting stages, the original form becoming
modified. Soon after conjugation these are flattened, with irregular
lateral boundaries, which become on the following day hexagonal. The
membrane becomes thickened, and presents tuberoulations at the
margin, but no secondary membrane is formed. Brought upon damp
earth, they soon become globular, and otherwise behave as ordinary
isospores.
In order to distinguish that which appertains to the cycle of alternation
of generations from the rest, the simple method is to start from the
fertilized germ, and see what are the modifloations which are essential
in order to arrive again at the same reproductive process. In this case
we have the isospore—it germinates—produce the vegetative plant,
which needs neither to divide, nor produce a sexual zoospore, nor to
become an ordinary zoosporange—it can directly produce spores. These
close the first generation. The second oospore generation oocnra in the
germination of these spores in the form of sexual zoospores, which
directly lead to the formation of the iaospore—the limits of two genera-
tions. All the rest are but phenomena of adaptation.
“ Thus, in nature, the vegetative plants in spring almost all become
zoosporangia, and spread the growth over considerable areas. Zoospores
which fall into the water are not lo s t; they acquire a double membrane,
and lie dormant until they chance mechanically to arrive on moist soil.
I f drought sets in, the plasma retreats to the roots ; if the earth be
some time a little moist, the root cells become hypnospores, awaiting
the rain in order to develop multitudes of zoospores ; but if the earth
becomes rapidly dried, the root cells remain unaltered, until a moistening
excites the formation of zoospores. A great many of the root cells can
manifestly accidentally reach tho surface of the soil, and thus, according
to the state of the moisture of the earth or of the air, sometimes ger.
minate, sometimes become zoospores.” All this in the spring. The hotter
months favour the formation of spores, but a t that time only the
vegetative plants are mostly to be found, either undergoing cell division
or spore formation. They can also furnish unioiliate zoospores without
becoming modified into ordinary zoosporanges.
Formation of ordinary zoospores may be accomplished in a fourfold
way—
1. From the vegetative plant. -
2. From the ordinary zoosporange.
3. From the root cell.
4. From the hypnosporange.
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