THALLOPHYTA: ALGAE 



65 



inner cells, respectively, of the young antheridium (Fig. 53.4). The 

 primary capituliim forms about six secondary capitnla. Each of these 

 gives rise to a pair of long filaments consisting of 100 to 200 small cells, 

 from every one of which a sperm is liberated (Fig. 53B). At maturity, 

 the entire antheridium falls apart. A single antheridium of Chara 

 produces 20,000 to 50,000 sperms. These are coiled and bicihate, 

 resembling the sperms of bryophytes. 



Fig. 52. Branch of Chara bearing an oogonium, with sterile jacket and crown, and an 

 antheridium, with interlocking, shield-like wall cells, X50. 



An oogonium is an enlarged apical cell. It produces a single large egg. 

 A unique feature of the oogonium is the presence of five elongated, 

 spirally wound cells that arise below and completely surround it (Figs. 

 52 and 53 A). At the top of the oogonium each jacket cell cuts off a small 

 cell, these five cells forming a crown. In Nitella each spiral cell cuts off 

 two crown cells, making ten in all. When the egg is ready for fertiliza- 

 tion, the spirally twisted cells separate shghtly just below the crown, 

 forming five slits through which the sperms enter the oogonium. After 

 a sperm nucleus has united with the egg nucleus, the walls of the sur- 

 rounding cells harden, the whole structure becoming nut-like. In this 

 condition the zygote rests. Before germination, the fusion nucleus gives 

 rise to four nuclei. Each probably has the haploid number of chromo- 

 somes, although this has not been definitely established. Three of these 



