104 PLANTS FOB THE 



lar ulva is one, if not the best of the algse used as an 

 ae'rator of the water for a tank ; and, when placed in the 

 gun, will soon be covered with innumerable minute bub- 

 bles of oxygen, which buoy it up in a very graceful man- 

 ner ; but, when a sudden cloud passes, before the sun, 

 the. bubbles will rise to the surface, and the frond fall 

 to the bottom. On dark- days, this plant, more than any 

 other, shows the want of the sun's light, and will re- 

 main dark and dull at the bottom of the tank, but 

 brightens again on the first sunny day. This plant goes 

 under several names, as sea-lettuce, from its resemblance 

 to the garden vegetable of that name ; oyster-green, be- 

 cause it is employed to cover oysters ; and green layer, as 

 it is employed for culinary purposes when another alga3 

 called Pprphyra cannot be procured, but it is not thought 

 to be so good as that. 



Ulva laduca is very much like the U. htissima in 

 appearance and properties as an aerator, for the tank, but 

 is not so common, and is of a lighter green color and 

 more tender in texture. 



Ulva linza is not near as common as the two former 

 plants, and is longer in proportion to its breadth. I have 

 a plant of about eight inches in length, growing on the 

 back of a Buccinum, or sea-snail, which the suicidal mol- 

 lusc turns upon when hungry, and it has consequently 

 become very shabby. It is a curious sight to see this shell- 

 fish travelling around the tank with this ocean tree upon 

 his back. I have seen snails with quite a forest of ulva 

 upon their shells. 



The JEnicromojyha compressa, or common sea-grass, is found 



