AQUATIC AI/G^:. SEA- WEEDS. 23 



Canary Islands, is of great importance as an article 

 of commerce ; and, when scarce, has been sold for 

 even a thousand pounds a ton. 



The purple powder, called Cudbear, that is used 

 in dyeing purple, is prepared from the Lichen tar- 

 ta'reus, which is common in many parts of Eng- 

 land ; but it can be used only for dyeing woollen 

 cloth, as it does not communicate its colour to 

 vegetable substances. 



The Aquatic Alga?, including the Sea-weeds, 

 imbibe all their nourishment through their surface, 

 the roots serving only to fasten them to the bottom ; 

 many of them, indeed, float about in the water, 

 without being attached to any solid body. They 

 constitute a very large tribe. 



Some of the Sea-weeds are used as food ; and all 

 are of great importance to farmers on the sea-coast, 

 for manuring their land. In the islands of Jura 

 and Skye, the Bladder-fu'cus, or Sea- wrack, Fu'cus 

 vesiculo'sus, often serves as winter food for the 

 cattle, which regularly go down to the shores, when 

 the tide is out, to eat it ; and even the deer have 

 been observed to come from the mountains, to 

 feed upon this plant. Linnaeus says, that the in- 

 habitants of Gothland in Sweden boil this fu'cus 

 in water, and feed their hogs with it, mixed with 

 meal : in Scandinavia, the poor people thatch their 

 cottages with it. But one of the most important 

 purposes to which this sea-weed is applied, in 



