OOGAMY IN VAUCHERIA. 



297 





or eight) days if transferred to a 2*0 to 4-0 per cent, solution of cane 

 sugar and exposed to bright light. In the variety F. repens the 

 female organs, the oogonia, are usually placed singly upon the 

 .thread, each being accompanied by only one male organ, the 

 antheridium. The oogonium is sessile on the thread, the 

 antheridium terminates a short curved branch. 



The oogonium is obliquely ovate (Fig. 110, o), densely filled with 

 plasma containing chlorophyll and oil, and is separated from the 

 thallus thread by a partition $ 



wall placed somewhat above 

 the base of the oogonial branch. 

 If an oogonium is observed at 

 the moment of its origin, it will 

 be seen that the contents of the 

 thread withdraw from those of 

 the rudimentary oogonium, in 

 exactly the same way as in the 

 formation of a sporangium (see 



ailtea). The OOgonium is pro- , antheridium : ch, chromatophores ; nl, oil- 



. , , . . drops. The nuclei n are represented, although 



Vlded With a Unilateral, beak- they are only visible after suitable staining 



like outgrowth, in which colour- ( x 240 ^ 



less protoplasm is collected. In advanced stages of development 

 this latter occupies the entire anterior part of the oosphere. If 

 now we observe such an oogonium uninterruptedly, we shall see 

 the colourless substance at the beak end put out a papilla-like pro- 

 jection, which rounds off more and more into an independent ball ; 

 this separates finally from the contents of the oogonium, and 

 passes out into the surrounding water, where it slowly goes to 

 the bottom. The membrane of the oogonium at the end of the 

 beak is swollen, and the resulting jelly is ultimately completely 

 dissolved. The remaining contents of the oogonium round off, its 

 colourless apex is the receptive-spot, or place of fertilisation. 



The antheridial branch is more or less strongly curved. Its 

 bent end is formed into an antheridium, and is cut off by a parti- 

 tion wall (Fig. 110, a). In the ripe condition it is distinguished by 

 its colourless contents, while the branch which bears it is rich in 

 chlorophyll. The antheridium usually turns its apex away from 

 the oogonium. In the colourless contents of the antheridium short 

 rodlets, arranged longitudinally, are more or less clearly distinguish- 

 able. At the moment when the oogonium extrudes a portion of 

 its colourless protoplasmic substance, the antheridium opens at its 



