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Related article: into the water by lateral openings in the walls of cells containing
them. They swim rapidly about, propelled by their cilia, and ere
long attach themselves to various objects and grow into Ulothrix
filaments. The sexual method of reproduction is effected through
the production of many gametes, in cells of the filament, which re-
semble the zoospores in shape but differ from them in being smaller
and possessing Online Celebrex but two cilia. These escape into the water, and,
after swimming about for a short time come together in pairs and
fuse with one another. The product of the fusion of each pair of
these like gametes is termed a zygospore. The zygospore swims
about but finally comes to rest, remaining quiescent for a consider-
able length of time. It then enlarges and its protoplasmic content
236 PHARMACEUTICAL BOTANY
divides to form several zoospores which, escaping from the cell,
swim about for a while and finally, attaching themselves to objects,
grow into filamentous Ulothrix organisms.
4. Order Conjugates. To this order belong the desmids and
pond scums which are distinguished from other green algae by
presenting no motile stages, in their life histories. They are all of
fresh-water habit and reproduce by conjugation.
Family Desmidacese. The desmid family includes a number of
genera of unicellular as well as filamentous green plants that present
a variety of shapes. Each unicellular desmid is characterized by
being composed of Online Celebrex two like halves frequently separated by each
other by a constriction called the isthmus. In each half there is a
chromatophore containing pyrenoids. The nucleus is found in the
isthmus. Reproduction is accomplished either asexually by fission
or sexually by conjugation.
Family Zygnemaceae. This is a family of pond scums including
the well-known genera, Spirogyra and Zygnema.
Spirogyra Online Celebrex or Brooksilk is a filamentous organism found suspended
or floating in masses in quiet water. Each filament when examined
microscopically will be found to consist of more or less elongated
cylindrical cells arranged end to end, the terminal cells having
rounded extremities. Each cell has a cell wall of cellulose within
which is to be found a thin film of ectoplasm. One or more spirally
shaped chromatophores will be seen directly within Online Celebrex this area. Each
chromatophore contains chlorophyll and a number of pyrenoids.
In the center of the cell the nucleus is found. Fine strands of
protoplasm hold it in place and run out to the ectoplasm.
Under favorable circumstances the cells of Spirogyra increase
rather rapidly in length. Abnormally long cells are not seen,
however, because the elongating cells speedily divide, forming two
daughter-cells. Under the best of conditions, division may occur
every night. In this way the filaments are rapidly made longer.
Sooner or later they break and in this way the plant multiplies.
Spirogyra has also a process of sexual reproduction known as
conjugation. This process occurs normally from March to June
and July, but can be induced in the laboratory by allowing the water
in the vessel in which it is growing to slowly evaporate. Two fila-
ments arrange themselves side by side, and the cells lying opposite
each other undergo internal changes so as to form gametes or sexual
cells. Each protrudes a process or conjugation tube; these unite
FIG. 114. Spitogyra sp. A, terminal portion of vegetative filament; B, stages
of scalariform conjugation; C, preparation for lateral conjugation; D, zygospores
formed by lateral conjugation. (Gager.)
and the protoplasm from one cell passes over and coalesces with that
in Online Celebrex the cell opposite. The result of the process is a new cell called a
zygospore or zygote. Online Celebrex This is set free by decay of the Online Celebrex walls of the old
2 3 8
cell and falls to the bottom of the water, there to undergo a resting
stage until favorable conditions for growth arise.
5. Order Diatomales. Family Diatomaceae. This family com-
prises several thousand species of unicellular plants called Diatoms
which are found in fresh, brackish and salt water, forming much of
the diet of small animals. While unicellular, they frequently are
united in colonies. They all possess chromatophores containing
PIG. 115. Two species of Diatoms. To left, Diatoma vulgare; a, side view of
frustule; b, frustule undergoing division. To right, Grammatophora serpentina:
a, front and side views of single Online Celebrex frustule; b, b, front and end views of divided
frustule; c, frustule about to undergo division; d, frustule completely divided.
chlorophyll but this green pigment is often obscured by the presence
also of a brown pigment.
The most striking peculiarity of the group is the structure of the
enclosing cell wall. This is in the form of a siliceous case consisting
of two valves which fit into each other like the halves of a pill box.
The valves, which are beautifully sculptured, are similar except that
one is slightly larger than the other so as to fit over it. Diatoms
vary in form being either circular, linear, elliptical, cylindrical,
rhomboidal, triangular or fan-shaped, etc. Some are borne on the
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