84 A TEXTBOOK OF THEORETICAL BOTANY 



caps at its upper end, each marking the position of a ring and equal in number 

 to the times the cell has divided. The occurrence of these cap cells m the 

 filaments makes Oedogoniiim easily recognizable. 



Reproduction is both sexual and asexual, the latter occurrmg durmg the 

 summer months under conditions favourable for growth, while the former, 

 since it results in the production of resting spores, is suitable for tiding the 

 Alga over periods unfavourable for growth, such as, for example, drought. 



Asexual Reproduction 



In asexual reproduction any cell of the filament may function. The 

 protoplast is withdrawn from the cell wall and forms a mass in the centre 

 of the cell (Fig. 65). One area at the side of this mass becomes colourless 



Fig. 65. — Oedogonium concatenatum. Stages in the liberation of a 

 zoospore. {.After Hint.) 



and round this numerous fine flagella are developed. The cell wall splits 

 across and the protoplasmic mass passes out through the opening. On 

 being liberated the zoospore slips out of the gelatinous membrane which 

 originally surrounded it and becomes spherical. There is no true wall around 

 the zoospore, for the whole mass is purely protoplasmic in structure. It 

 swims by means of the flagella, possesses an eye spot and is sensitive to light 

 in just the same way as we have described in the case of Ulothrix. After 

 swimming for an hour or so it settles down on its colourless end, withdraws 

 its flagella and secretes a cell wall. The free end grows out and is divided 

 by a transverse wall, thus beginning a new filament. The colourless portion 

 usually develops into the branched holdfast cells. 



