Usually two cilia are present; in Botrydium and Hydrodictyon only one is present; in certain species of Cladophora four; in Dasycladus a chaplet, and in Oedogonium a ring of many cilia.
In the zoosporangia of Oedogonium, Tetraspora and Coleochaete the contents become transformed into a single zoospore.
The escape of zoospores is effected by the degeneration of the sporangial wall (Chaetophora), or by a pore (Cladophora), a slit (Pediastrum), or a circular fracture (Oedogonium).
In certain species of Oedogonium minute male plantlets, known as dwarf males, become attached to the female plant in the neighbourhood of the oogonia, thus facilitating fertilization.
Indeed the genus Oedogonium exhibits a high degree of specialization in its reproductive system, considering that its thallus has not advanced beyond the stage of an unbranched filament.
Such are Coleochaete, Oedogonium, Cylindrocapsa, Ulothrix, Vaucheria, Volvox, &c. In others only the asexual method is yet known.
In rare cases the oosphere has been known to germinate without fertilization (Oedogonium, Cylindrocapsa).
Oedogonium sp., oogonium antheridium at a node on at moment of fertilization a lateral appendage.
Oedogonium sp., zoospore K1.
In Sphaeroplea it is only at this stage that zoospores are formed at all; but in most cases, such as Oedogonium, Ulothrix, Coleochaete, similar zoospores are produced again and again upon the thallus, and the product of the oospore may be regarded as merely a first brood of a series.
There is, however, considerable variation in the nature of the membrane in different species; thus the cell-wall of Oedogonium, treated with sulphuric acid and iodine, turns a bright blue, while the colour is very faint in the case of Spirogyra, the wall of which is said to consist for the most part of pectose.
Oedogonium, Coleochaete), the Bryophyta, and the simpler Pteridophyta, such as Phylloglossum, have been regarded as illustrating the method of progression, though there is no reason to regard the existing forms as constituting an actual series.
In the Algae, such as Fucus, Volvox, Oedogonium, Bulbochaete, and in the Fungus Monoblepharis, the spermatozoid is a small oval or elongate cell containing nucleus, cytoplasm and sometimes plastids.
In some cases the region where the penetration of the male organ takes place is indicated on the oosphere by a hyaline receptive spot (Oedogonium, Vaucheria, &c.), or by a receptive papilla consisting of hyaline cytoplasm (Peronosporeae).
The resemblance between this genus and Oedogonium among the algae is very striking, as is also that of Myrioblepharis and Vaucheria.
Oedogonium sp., intercalated growth by insertion of new piece(a) n., nucleus; p.v., pulsating vacuoles; e.s., eyespot.
In Ulva and Mesocarpus the chromatophore is a single plate, which in the latter genus places its edge towards the incident light; in Spirogyra they are spiral bands embedded in the primordial utricle; in Zygnema they are a pair of stellate masses, the rays of which branch peripherally; in Oedogonium they are longitudinally-disposed anastomosing bands; in Desmids plates with irregular margins; in Cladophora polyhedral plates; in Vaucheria minute elliptical bodies occurring in immense numbers.
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