LESSON XVI 



VAUCHERIA AND CAULERPA 



STAGNANT ponds, puddles, and other pieces of still, fresh 

 water usually contain a quantity of green scum which in the 

 undisturbed condition shows no distinction of parts to the 

 naked eye, but appears like a homogeneous slime full of 

 bubbles if exposed to sunlight. If a little of the scum 

 is spread out in a saucer of water, it is seen to be com- 

 posed of great numbers of loosely interwoven green 

 filaments. 



There are many organisms which have this general naked- 

 eye character, all of them belonging to the Algtz, a group 

 of plants which includes most of the smaller fresh-water 

 weeds, and the vast majority of sea-weeds. One of these 

 filamentous Algce, occurring in the form of dark-green, 

 thickly-matted threads, is called Vaucheria. Besides occur- 

 ring in water it is often found on the surface of moist soil, 

 e.g., on the pots in conservatories. 



Examined microscopically the organism is found to consist 

 of cylindrical filaments with rounded ends and occasionally 

 branched (Fig. 38, A). Each filament has an outer cover- 

 ing of cellulose (B, c.w) within which is protoplasm con- 

 taining a vacuole so large that the protoplasm has the 



