A WORLD IN THE WATER 97 



outfalls. Sometimes they grow so thickly as to 

 threaten to block up channels where the water- 

 way is narrow and shallow. 



Some of the marine species of Cladofhora 

 are pretty little greenish brown plants which are 

 often found in abundance in pools which have 

 been left by the tide. These green seaweeds 

 are usually very bushy in habit, and their 

 charming manner of growth is plainly seen if 

 they are floated out on to a piece of white 

 paper. A single group of the green seaweed 

 is that which is represented by the Rmdaria, 

 a plant which is often responsible for bring- 

 ing about a terribly slippery condition of the 

 rocks. If examined, it will be found that the 

 growth of this species is usually in the form of 

 small roimded masses. 



In many of the green seaweeds the actual 

 manner of reproduction is not very clearly 

 known, but in the case of the Sea Lettuces 

 {Ulva) a prominent method adopted seems to 

 be on the following Unes. When all circum- 

 stances are favourable for reproduction, a 

 change takes place in the contents of the 

 cells which go to the formation of the plant. 

 These undergo certain alterations, and even- 



