JUNE. 10] 



substance, and innumerable insects find a covert 

 under it. The lesser species {lemna minor) is 

 very common, and has small compact leaves, 

 very thick in their texture, and slightly con- 

 vex beneath. It grows so rapidly, as some- 

 times to be a troublesome plant in the pond ; 

 but it has been discovered that it converts 

 hydrogen gas into air fitted for respiration, and 

 thus renders the exhalation from the stagnant 

 pool less injurious to the neighbourhood. The 

 flowers of the duckweed are so inconspicuous, 

 that few would observe them, and the greater 

 duckweed, (Jemna jwli/hrhr/,) though some- 

 times covering our ponds with its purple fronds, 

 is not known to flower in Britain. 



Several species of the plant, called pondweed, 

 (potamoffefon,) are now wearing their green 

 flowers, which rise above the water, while the 

 whole of the foliage is immersed, and floats 

 about on our clear streams, looking as beau- 

 tiful as the delicate green seaweeds which lie 

 in the ocean. These plants are often very 

 thick in the pools, and when the current is 

 slow, are sometimes several feet in length ; but 

 they grow in the Swiss lakes so much larger 

 and thicker, that they look like large woods 

 under the water, and are frequently twenty 

 fathoms in length. Like other aquatic plants, 

 they shelter many insects, and swans and 

 ducks are very fond of them. 



Loudon quotes professor Martyn's observa- 

 tion on water plants generally, that the " res- 

 piration of these truly aquatic vegetables must 



