GREEN ALGAE 



397 



pairs (Fig. 335, i.). In Bryopsis the size is unequal (ii.) ; while Codium 

 shows still greater inequality (iii.). This is again more marked in 



FIG. 335. 



Gametes of various Siphonales, and Siphonocladiales, illustrating differentiation 

 of male and female. i=Acetabularia, isogametes ; ii = Bryopi>is ; iii Codium; 

 iv Sphaetoplea ; v = Vaucheria. In iv. and v. the large egg is stationary, while 

 the smaller spermatozoid is motile. (Taken from Oltmanns' Algae.) 



Sphaeroplea, where the large egg is non-motile (iv.), a condition still 

 more accentuated in Vaucheria (v.), which is the most advanced of 

 all in sexual differentiation. 



The sex-organs of Vaucheria arise 

 close together as short lateral branches 

 (V. sessilis), or borne together on the 

 same branch (V. terrestris, Fig. 336). 

 The anthendia are horn-like, curved 

 bodies, the oogonia are oval. In the 

 antheridium a septum cuts off the 

 multi-nucleate protoplast from the 

 parent tube : each nucleus becomes the 

 centre of a spindle-shaped sperma- 

 tozoid ; and these escape, with their 

 paired cilia pointing fore and aft, 

 through an opening at the distal end. 

 The oogonium also at first contains 

 numerous nuclei embedded in proto- 

 plasm stored with many globules of oil. 



But, as the OVUm matures, all the nuclei 



but one wander back into the parent 



FIG. 336. 

 Sexual branch of Vaucheria terrestris, 



