ALGAL AND FUNGAL PROTISTS 25 



such as PytJiium. Such organisms are termed coenocytes 

 (Gr. &omos=shared in common). 



Those who can recall their early botanical studies may 

 remember what happens when a Vaucheria is incised under 

 water ; part of the protoplasm oozes out in lobed masses, 

 which show amoeboid movements for from half an hour to 

 an hour. A sharply, often doubly contoured skin-layer or 

 ectoplasm, like that seen in the mycetozoan plasmodium is 

 the surface of this naked protoplasm, portions of which 

 may become detached as rounded bodies, in which vacuoles 

 appear. The layer of protoplasm limiting a vacuole is called 

 the vacuolar membrane or tonoplast. Many of the amoeba- 

 like fragments disintegrate, but some which contain nuclei 

 renew their growth and secrete a new cell-wall. When 

 Vaucheria sessilis is grown in water in sunlight vegetative 

 reproduction by zoogonidia occurs. These are multinucleate 

 bodies with a pair of flagella opposite each nucleus. A 

 terminal part of a filament is shut off by a septum before 

 the zoogonidium is formed, and the motile body escapes by 

 an aperture in the cell-wall. This happens when the plant 

 is exposed to light after being in the dark for some hours. 



After swimming awhile the zoogonidium sinks, loses its 

 cilia, secretes a cell-wall, and germinates by one or more 

 sprouts. The zoogonidium remains as a permanent part of 

 the thal]us thus developed. 



Sexual reproduction is by gametangia : an antheridium 

 and one or two oogonia are formed as lateral branches shut 



