GREEN ALCiAK 



cell-wall. After a period of rest it germinates, the coiUents dividiiit;, 

 and escaping as zoospores, which grow into new lilamcnts. 



Ulothrix takes a low place both as regards structure and propagativc 

 method. The differentiation of its sexual cells is imperfect. N,,t 

 only is there no distinction of sex in the form of the gametes, lnjt 

 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 (synganiy) 

 is a means of strengthening otherwise weak cells, which were originally 

 organs of vegetative propagation. 



Oedogonium and Bidbochaete are also hlamentous Algae, but with 

 more elaborate structure of their cells. Various species are very 



i-'iG. 331. 



Oedogonium. J=escapino zoospores, if = free zoospores. C"-^ sexual orKajiM 

 before fertilisation. D = in process of fertilisation. O = oogonia ; a dwarf iiult-^. 



S = spennatozoid. (After Pringshcini, from StrasburRor.) ( ■ 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 settlt<. 

 forms a cell-wall, and grows directly into a new individual. i 

 plants are readily distributed by this means. The sexual ori;.ui' 

 of Oedogonium are anthcridia and oogonia, which differ in size. The 

 oogoniimi 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 ODum remains in siin, and is motionless (Fig. 331, C, D). At 

 the same time cells, of the same or of a separate filament, undergo 



