THE GREEN FELT: VAUCHERIA. 1 23 



oogonium, as shown in the figure, is usually turned somewhat to 

 one side. When mature the pointed end opens and a bit of the 

 protoplasm escapes. The 

 remaining protoplasm 



forms the large rounded /M^^li 



egg cell which fills the wall 

 of the oogonium. In 



some of the o< igonia which ^MS^¥ « \ 



we examine this egg is sur- 

 rounded by a thick brown „ . . .,. Flg - ' 8 ; . . . 



J Vauchena sessilis ; oogonium opening and emit- 



wall, with Starchy and oily ting a bit of protoplasm ; spermatozoids ; sperma- 



J J tozoids entering oogonium. (After Pringsheim and 



contents. This is the fer- Goebei.) 



tilized egg (sometimes called here the oospore). It is freed 

 from the oogonium by the disintegration of the latter, sinks 

 into the mud and remains here until the following autumn 

 or spring, when it grows directly into a new plant. The 

 spermatozoids are very difficult to see and one should not expect 

 to study them here. Fertilization is brought about by the 

 spermatozoids swimming in at the open end of the oogonium, 

 when one of them makes its way down into the egg and fuses 

 with the nucleus of the latter. 



210. Vaucheria compared with spirogyra. — In vaucheria 

 we have a plant which is very interesting to compare with 

 spirogyra in several respects. In spirogyra growth takes place 

 in all cells, that is in all parts of the thread, while in vaucheria 

 growth is confined to the ends of the threads and the ends of 

 the branches. This is a distinct advance on spirogyra. Again 

 in spirogyra any part of the thread (any cell) may become one 

 of the sexual organs. In vaucheria the sexual organs are 

 special branches, which are short, and further, the two organs 

 are different in size so that they can readily be distinguished 

 long before the time for fertilization. Then in vaucheria the 

 supplying cell does not give all its content to the receiving cell, 

 but only a bit of the protoplasm in the form of a minute body, 

 the spermatozoid. > 



