Flowers. 



163 



as sex cells, but they are entirely alike, and cannot be con- 

 sidered as distinctly male and female. 



118. Reproduction in Oedo- 

 gonium. — In Oedogoniiim, 

 which is another low form of 

 plant growing in water, there 

 is a very marked difference in 

 the two cells which unite. By 

 reference to Fig. ?,6 this will 

 be made clear. The plant 

 body consists of a multicellular 

 filament. Certain of the cylin- 

 drical cells of the filament grow 

 into the form of spheres (termed 

 oogottia ; singular, oogonuwt), 

 and become gorged with food 

 materials. In some species 

 others of the cylindrical cells 

 divide to form shorter cells 

 whose protoplasts also divide 

 each to form two protoplasts 

 having power of locomotion by 

 means of cilia. These pass 

 through openings in the walls 

 of the parent cell, swim to 



and enter an oogonium, and one of them fuses with its 

 protoplast. A thick wall is now formed about the fused 

 protoplasts, and the body thus protected is known as a 

 resting spore. After a time, depending to a certain extent 

 on external conditions, the resting spore divides to form 

 four ciliated motile bodies, each of which finally grows to 

 be a filamentous plant like the parent. In Oedogonium, 

 therefore, sexuality has become clearly developed. One 



Reproduction in Ulothrix zonata. 

 I, a young filament; 2, four cells of 

 a filament whose protoplasts have 

 divided to form small zoospores, 

 seen escaping from two of the cells ; 

 3, protoplasts escaping to form large 

 zoospores; 4 and 5, the fusion of 

 two small zoospores ; 6, a large 

 zoospore. After DODEL-PORT. 



