THE LIME-WOKT FAMILY. 



97 



and glass. Since barilla" has been used for these purposes 

 the burning of sea-wrack has almost ceased. From the 

 alkali of sea-weeds an important chemical substance called 

 *' iodine'^ is obtained, which is well known in medicine and 

 the arts as a powerful absorbent. In agricultural districts, 

 *' wrack'''' is eagerly sought after for manure ; its virtue as 

 such depends principally on the salt it contains. 



Gulf-weed (Sargassum hacciferum). A deep-sea weed, its 

 fronds rising from a great depth, and covering the surface of 

 the ocean for thousands of square miles. It is found in the 

 meridian of 40'' W., and between the latitudes of 20" and 

 45^ N. 



Trumpet sea-weed (Laminaria huccinalis). The stems of 

 this species attain the height of six or more feet, being nar- 

 row at the base but widening upwards, and bearing long, 

 broad, leafy fronds, which " float on the surface. The stems 

 are cut into lengths, and used as a curiosity trumpet. De- 

 prived of its alkaline properties by a chemical process, it 

 becomes tough and plastic, like morocco leather, and is then 

 used for binding albums. By other processes it becomes 

 hardened, and is then used for walking-sticks, whips, and 

 knife-handles ; also as a substitute for stag-horn. 



The Lime -wort Family. 



(Charace^.) 



Small fresh-water plants, having articulated stems and 

 branches which grow in whorls, either transparent or coated 

 with carbonate of lime. The organs of reproduction consist of 

 globose nut-like bodies of two sizes, covered by spiral tubes, 

 which give them a striated appearance. 



This singular family comprises about thirty described 

 species, found in stagnant water in most parts of the world. 

 They grow very rapidly, and soon fiU shallow waters, some- 

 times forming great masses which decay and become offen- 

 sive, causing malaria in many districts, as in the Pontine 

 marshes near Rome. They have no knowQ uses, and must 



H 



