98 



A TEXTBOOK OF THEORETICAL BOTANY 



nuclei, oil and chloroplasts, though ultimately only a single central nucleus 

 remains, which reaches a considerable size. The rest migrate back mto the 

 filament. The whole oogonium then becomes cut off from the rest of the 

 coenocyte by a transverse wall or septum. Later a beak, or lateral swelling, 

 is developed at one side of the oogonium, and in this region the wall becomes 

 gelatinous and dissolves, leaving a pore. It is at this point that, subsequently, 

 the antherozoids enter the oogonium. When mature the chloroplasts and oil 

 take up a central position, leaving either a clear peripheral area of protoplasm 



FEMALE 

 NUCLEUS 





60 



•••S-O 



•»*el? 



MALE 

 NUCLEUS 



FEMALE 

 NUCLEUS 



FUSION 

 NUCLEUS 



Fig. 79. — Vaucheria sessilis. Maturation of the oogonium. A, Young stage. B, Nuclei 

 returning from oogonium to filament. C, Oosphere at fertilization stage. D, 

 Oospore. {After Oltnumm.) 



or at least a clear area under the beak, the receptive spot, and the contents 

 as a w'hole contract and become the oosphere (Fig. 79). 



The antheridia are formed at the ends of short lateral branches and 

 develop simultaneously with the oogonia (Fig. 80). Each antheridium is 

 an elongated, strongly curved structure and is cut off from the thallus by a 

 septum. The nuclei within the antheridium divide up and ultimately each 

 becomes surrounded by a small mass of cytoplasm and constitutes an 

 antherozoid. These antherozoids form a mass in the centre of the 

 antheridium, whilst the periphery is filled with chloroplasts and residual 

 cytoplasm. The antherozoids are liberated apically shortly before daybreak, 

 1 minute, colourless, oval bodies with two laterally inserted flagella. 



