224 



THALLOPHYTES. 



forms a cell-wall of its own. These spores do not fall out ; they either become freed by 

 the decomposition of the sporangium-wall, or they fall off together with the sporangium ; 

 some days after their formation they put out one or two germinating-tubes. The spores 

 of F. hamata are formed in the same manner, but after their formation the sporangium 

 splits at its apex, the spore slips out with a jerk and remains at rest, to germinate the 

 next night. In several other species (as V. sessilis, sericea, a.nd piloboloides) true zoospores 

 are formed. The preparations for them are similar to those in the last case ; but the 

 contents of the branch which has swollen into a zoosporangium do not become sur- 

 rounded by a cell-wall, but contract, showing in the interior one or more vacuoli, and 

 then escape as a naked cell from a fissure at the apex of the branch (Fig. 158, j4, sp'). 

 The escaped primordial cell contains numerous grains of chlorophyll surrounded by 

 a layer of colourless protoplasm, and is everywhere covered by delicate densely crowded 

 short cilia. Their vibratile motion causes a movement of the large ellipsoidal zoospore 

 (as much as ^mm. long) about its longer axis, which sometimes, however, (as in 

 V. sericea,^ lasts only for ^ to i§ minute. In F. sessilis the rotation begins, as I have 



Fig. i^B.—Vattcheria sessilis (X about 30). 



distinctly seen, during the escape from the sporangium ; and if the opening is too small, 

 the zoospore splits into two pieces; both become rounded off; the outer piece rotates 

 and swims out, while the inner piece rotates within the sporangium. As soon as the 

 zoospores come to rest, the cilia disappear, and a cellulose-wall is produced (Fig. 158, B). 

 The formation of the zoosporangia generally begins in the night ; the spores escape in 

 the morning, and their germination commences the next night. The spore puts out 

 either only one or two tubes (C, X)), or it forms on the other side at the same time a 

 root-like organ of attachment {E, F, «u;). The Sexual Reproduction is brought about by 

 oogonia (female cells) and antheridia (male cells). Both originate as twig-like protuber- 

 ances from a branch or stem (Fig. 159, yl, B), sometimes even on the germinating tube 

 of the zoospore (Fig. 15S, F, og, b). All the species of Vaucheria are monoecious, and the 

 two kinds of sexual organs are mostly found very near together. The Antheridia usually 

 arise ^ as the terminal cell of a branch by its transverse division, and contain very little 



* In the Vaucheria synatidra discovered by Woronin living in brackish water 2-7 small horns 

 (antheridia) arise on the large ovoid terminal cell of a two-celled branch (Bot. Zeitg. 1869, nos. 9, 10). 



