176 



CBTPTOGAMS 



a 



00 - 



n 



the protrusion of one or two tiibular filaments, wliicli 



grow directly to new plants. 



425. Zoospores are apt to be formed when the plant is 



C'rowiiio- in a submei'2'ed situation. In I'l'^ces where it is 



exposed to the air and moistened only occasionally, as by 

 the dew, a second method of rejaro- 

 cluctiou prevails. SAvellings arise 

 on the thallus, which develop into 

 short, thick branches of peculiar 

 form. "When cut off by septa 

 below they become the oiiijonia 

 (Fig. 200, og'). The contents of 

 the oogonium Cdiitracts somewhat 

 to form the egg cell, and an open- 

 ing makes its appearance in the 

 Oogonium wall. Near by, short, 

 slender, often coiled branches grow 

 up. Their extremities are cut off 



290. V;iiii-lii'i-ia: J, the im- 

 opeued antberidiuDi 

 (o) and Oficjoniuin 

 (og) ; B, the same 



.after fertilization . 



and formation of to form thc CDltln'ridui (Ing. 290, a), 



from which coitherozoicfs, bodies 

 resemblinfT small 



the oospore (os) . 

 Peingsheim. 



zoospores, are 

 finally liljcrated. The latter make their way througli 

 water to the opening of the oogonium, and one, enter- 

 ing, fuses with the egg cell. The resulting body, or 

 oospore, now surrounds itself ^vith a cell wall and enters 

 a resting state. It is ultimately set free by tlie rupture 

 of the oogoiiium 'ivall, and germinates. 



426. In Vaticheria we liave essentially the same reproductive pro- 

 cesses as in Ulotlirix, but liow appearing in a much modified foi-ni. 

 The single large zoospore of Vaucheria, with its many cilia, peilmnis 

 tlie same office as the numerous suuill zoospores of Ulothrix. 'I'lie pio- 

 dnction of the oospore in Vaucheria may lie likened lo the imion of 

 reproductive cells in Ulothrix, with the important difleieiice that now 

 the fusing' cells differ greatly in size, ami only one of them is niutile. 



427. Cells designed for re|iroductive union are called {/rnneles. 

 When they are of unequal size, the larger is termed er/ij cell or simply 

 f'fjff : the smaller, if motile, is an anthernzoid. The egg is said to be 

 f-nili-ed by the antherozoid. The liody directly resulting from the 

 union of unequal gametes is an oixyjore. 



