10 BRITISH CHAROPHTTA. 



obtained a hold and darkened the water, it has often 

 entirely disappeared. Some species are curiously- 

 intermittent in their occurrence, disappearing in a 

 locality altogether, and reappearing after some years, 

 the oospores evidently retaining their vitality for a 

 long period. 



It is difficult to account for the introduction of these 

 plants to newly-made pieces of water by any other 

 explanation than that the oospores, or portions of old 

 stems, are carried in mud on the feet of birds, although 

 this method of seed-dispersal has been discredited by 

 some authors. 



The principal enemies of the Charophytes belong to- 

 the vegetable kingdom. Apart from their competitors 

 for space and light among the higher water-plants,, 

 already alluded to, they are peculiarly liable to be- 

 strangled or stifled by filamentous and encrusting 

 Algse, which are frequently found growing among and 

 upon them. Dr. Griesenhagen states that he has found 

 instances of the root-bulbils of Ghara aspera being 

 attacked by a species of fungus, the interior of the 

 globular cell being filled by mycelial threads. In 

 one bulbil he detected animal organisms which he- 

 describes as " anguillula-like." Dr. Allen found that 

 the bulbils of this species were eaten by ducks. The 

 plants are often infested with Infusoria. "We have seen 

 one caddis-case built-up entirely of the ripe oospores- 

 of a Ghara, and stems and branchlets are sometimes^ 

 used for that purpose. It has been stated that Charo- 

 phytes are eaten by molluscs, but we have met with 

 no indication of this, though the plants are freely used 

 by them as a medium of travel. 



Many Gharas have an extremely unpleasant smell,, 

 said to be that of sulphuretted hydrogen, and Dr> 



