42 



CHLOROPHYCEAE 



forme. Sexual reproduction in all three species is isogamous in 

 character and the plants are monoecious. In H. patenaeforme the 

 zygote is motile for a short time, but in the other two species it 

 is always non-motile. At germination the zygote enlarges and 

 divides by meiosis into four biflagellate swarmers which first come 



Fig. 31. Hydrodictyon. A-F, development of young net of H. patenaeforme 

 from the zygote. A, young polyhedron. B, older polyhedron with four nuclei. 

 C, protoplasm granular just before zoospore formation. D, "pavement" stage. 



E, zoospores rounding off and wall of polyhedron expanding to form vesicle. 



F, fully formed net still enclosed in vesicle. (A-E x 250, F x 175,) G, portion of 

 mature net of H. reticulatum. H, polyhedron and young net of H. reticiilatum. 

 J, H. reticulatum, formation of net in parent cell from zoospores. (A-F, after 

 Pocock; G, H, after Oltmanns; J, after Fritsch.) 



to rest and then develop into polyhedral cells. After resting for a 

 period these divide to produce zoospores ; the food material in the 

 angular thickenings of the polyhedrons is used up and all the 

 swarmers are finally liberated in a vesicle, in which, after a period 

 of motility, they come together to form a new coenobium. The 

 vegetative plant is therefore haploid and its development is probably 



