. Elementary botany. Botany. 102 MORPHOLOG Y. forms two spermatozoids (sometimes only one) which are of the same form as the zoogonidia but smaller, and yellowish instead of green. In some species a motile body intermedi- ate in size and color be- tween the spermatozoids and zoogonidia is first formed, which after swimming around comes to rest on the oogonium, or near it, and develops what is called a "dwarf male plant " from which the real spermatozoid is / produced. 243. Oogonia. — The Fig. gS. Portion of tliread o f cedogonium showing antheridia. Fig. (39. Portion of tliread of ce
. Elementary botany. Botany. 102 MORPHOLOG Y. forms two spermatozoids (sometimes only one) which are of the same form as the zoogonidia but smaller, and yellowish instead of green. In some species a motile body intermedi- ate in size and color be- tween the spermatozoids and zoogonidia is first formed, which after swimming around comes to rest on the oogonium, or near it, and develops what is called a "dwarf male plant " from which the real spermatozoid is / produced. 243. Oogonia. — The Fig. gS. Portion of tliread o f cedogonium showing antheridia. Fig. (39. Portion of tliread of cedo- gonium showing upper half oogonia are formed di- tozmd,eady'toenter^^(After rectly from one of the Oltmans). vegetative cells. In most species this cell first enlarges in diameter, so that it is easily detected. The protoplasm inside is the egg cell. The oogonium wall opens, a bit of the protoplasm is emitted, and the spermatozoid then enters and fertilizes it (fig. 99). Now a hard brown wall is formed around it, and, just as in spirogyra Fig 100. Male nucleus just entering egg at left side. Fig. loi. Male nucleus fusing with female nucleus. Fig. 102. The two nuclei fused, and fertilization complete. Figs. 100-102.—Fertilization in cedogonium. (After Oltmans). a,nd vaucheria, it passes through a resting period. At the time of germination it does not produce the thread-like plant again directly, but first forms four zoospores exactly like the zoogonidia (fig. 103). These zoospores then germinate and form the plant. 244. (Edogonium compared with spirogyra.—Now if we compare cedo- gonium with spirogyra, as we did in the case of vaucheria, we find here also that there is an advance upon the simple condition which exists in spiro- gyra. Growth and division of the thread is limited to certain portions. The sexual organs are differentiated. They usually differ in form and size from the vegetative cells, though the oogonium is simply a changed vegetative. Please note that the
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