THALLOPHYTA: ALGAE 



75 



cell and about 1 ,500 small cells, each of which produces a sperm. Although 

 the sperms are laterally biciliate, one cilium is very short. The oogonia 

 are borne in groups of about 25 to 50 on both sides of the female plants 

 (Fig. 615). The groups are not surrounded by sterile cells. Each 



Fig. 62. Zonaria farlowii. A, portion of thallus with numerous groups of sporangia, 

 Xl}i; B, young sporangium with eight free nuclei; C, mature sporangium, the eight 

 aplanospores cut off by walls; D, young antheridia; E, young oogonia; F, mature antheridia; 

 G, two mature oogonia; B to (?, X300. (After Haupt.) 



oogonium consists of a small stalk cell and a single large nonmotile egg. 

 The eggs are discharged into the water and there fertilized. The zygote 

 gives rise to the sporophyte without undergoing any resting period. 



Zonaria. Zonaria has about the same distribution along both coasts of 

 North America as Dictijota. The thallus consists of an erect fan-like 

 cluster of thin flat branches arising from a stalk-like portion that is 



