. Botany of the living plant. Botany. GREEN ALGAE 393 cell-wall. After a period of rest it germinates, the contents dividing, and escaping as zoospores, which grow into new filaments. Ulothrix takes a low place both as regards structure and propagative method. The differentiation of its sexual cells is imperfect. Not only is there no distinction of sex in the form of the gametes, but occasionally the gametes may themselves germinate without fusion. They are strikingly similar in form and origin to the zoospores. The facts are in accord with the theory that fusion of gametes (syngamy) is a mean
. Botany of the living plant. Botany. GREEN ALGAE 393 cell-wall. After a period of rest it germinates, the contents dividing, and escaping as zoospores, which grow into new filaments. Ulothrix takes a low place both as regards structure and propagative method. The differentiation of its sexual cells is imperfect. Not only is there no distinction of sex in the form of the gametes, but occasionally the gametes may themselves germinate without fusion. They are strikingly similar in form and origin to the zoospores. The facts are in accord with the theory that fusion of gametes (syngamy) is a means of strengthening otherwise weak cells, which were originally organs of vegetative propagation. Oedogonium and Bulbochaete are also filamentous Algae, but with more elaborate structure of their cells. Various species are very. Oedogonium. .J =esf:apiuy zoospores. S —free zoospores. C = se.\ual organs before fertilisation. D = in process of fertilisation. O = oogonia; a —dwarf-males. 5=spermatozoid. (."^fter Pringsheini, from Strasburgcr.) (:-350.) commonly found attached to stones or submerged parts of plants in quiet fresh water. Their cells are uninucleate, and contain a single reticulate chromatophore. They may be propagated by zoospores, which are formed from the whole content of a cell ; it escapes through a transverse slit in the wall into water, having an oval form, with a fringe of cilia round the colourless anterior end (Fig. 331). After a period of movement the zoospore settles, forms a cell-wall, and grows directly into a new individual. The plants are readily distributed by this means. The sexual organs of Oedogonium are antheridia and oogonia, which differ in size. The oogonium is a large barrel-shaped cell, containing a single egg. It opens at maturity by a transverse slit, as in the liberation of the zoospores ; but the ovum remains in situ, and is motionless (Fig. 331, C, D). At the same time cells, of the same or of a separate filament, undergo. Pleas
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
