60 



MANUAL OF BOTANY 



two gametangia. The protoplasm of each undergoes rejuve- 

 nescence to form the gamete, and one of them passes over into 

 or through the tube and fuses with the other gamete, which 

 either enters the tube to meet the first or remains in its game- 



tangium, where it is joined 



Fia. 808. 



by the other. The first 

 condition is found in Zy- 

 gogoniv/m, and as there 

 is no difference between 

 the gametes taking part, 

 we cannot speak of differ- 

 ence of sex. In Spirogyra 

 (fig. 807) the cell which 

 passes over through the 

 tube begins to be diffe- 

 rentiated slightly sooner 

 than the other and may 

 be held to be the male 

 one. 



In CEdogonium sexu- 

 ality is completely esta- 

 blished, antherozoids and 

 oospheres being produced. 

 In some cases the whole 

 contents of the antheri- 

 dium forms a single an- 

 therozoid, which is cili- 

 ated. 



Unicellular forms 



occur in this group in 

 the family of the Desmids. 

 These are cells of bright- 

 green colour and usually 

 peculiar shape. Their 

 colouring matter is col- 

 lected into curiously 

 formed ohloroplasts, 



which may occur as 

 bands stretching the 

 whole length of the cell, 

 and having pyrenoids embedded in them. They multiply chiefly 

 by fission, as do the Diatoms, to which group they present 

 certain resemblances. Occasionally two individuals conjugate 



Fig. 808. A. Middle part of a sexual filament 

 of GSdogonium ciliatum, og, og. Oogonia 

 fertilised by the dwarf male plants, m, m, 

 developed from zoospores formed iu the 

 cells, n (antberidium), at the upper part of 

 the filament. B. Ripe oospore, c. Piece 

 of male filament of a species of (Edogo- 

 niiim, with productioQ of antherozoids, z, z. 

 D. The four zoospores resulting from an 

 oospore. E. Zoospore at rest. After 

 Pringsheim. 



