76 PRACTICAL BOTANY. 



for some time previous to the examination. Mount some 

 in water without a cover glass and look for filaments with 

 enlarged ends. If present, find as many different stages 

 of development as possible. This is the asexual mode of 

 reproduction. The ends of the filaments enlarge and be- 

 come cut off from the rest of the filament by a septum ; 

 the protoplasmic contents assume an ovoidal form and 

 become invested with cilia arranged in pairs; the end 

 of the filament opens, and the zoospore swims out by the 

 action of its cilia. The motion of the zoospore may con- 

 tinue for only a few minutes, or it may last for some 

 hours. As soon as it comes to rest it loses its cilia, 

 develops a cell wall, and grows into a new plant. The 

 observer who succeeds in finding these zoospores is re- 

 warded by the sight of one of the most beautiful objects 

 in the plant world. The zoospores are gonidia. 



The observation of the formation of zoospores in a spe- 

 cies of Vaucheria by the botanist linger in 1826 was the 

 discovery of the fact that certain plants pass through a 

 motile stage in their existence. The discovery of proto- 

 plasm and the correction of the older idea that the cell 

 walls possess life was a natural sequence to this discovery. 

 No other discovery has had so much to do with the revo- 

 lution that botanical science has undergone in the last 

 half century. 



10. Find filaments bearing the sexual reproductive or- 

 gans. In most species of Vaucheria both the male and 

 female organs are borne on the same filament, i.e., the 

 plants are monoecious. These organs originate as lateral 

 branches near together on the same side of the filament. 

 (See Fig. 35, c and d.) 



As the oogonium matures, it assumes a shape that has 

 been described as "like a bird's head"; a septum forms 

 at its base which separates it from the filament, thus form- 

 ing the ovary ; its distal end becomes gelatinized and 



