536 MANUAL OF NATURAL HISTOEY. 



or tubular, unsymmetrical ; fronds of one or 

 many cells, often united by gelatinous mat- 

 ter ; reproduction by single spores, contained 

 in superficial cells, which are scattered through 

 the whole frond, or situated in particular 

 parts of it. Distribution universal ; marine 

 or fresh- water. Some attain a considerable 

 size, as Scytosiphon filum of the North Sea, 

 or Macrocystis pyrifera of the Pacific, the 

 latter said to be occasionally upwards of 1 000 

 feet in length ; Sargassum hacciferum, met 

 with in large floating masses, is known as gulf- 

 weed ; "kelp," employed in the manufacture 

 of glass and soap, is composed of the ashes of 

 Fucus vesiculosus, F. serratus, and F. no- 

 dosum, the kind which is used for obtain- 

 ing Iodine and Bromine, is chiefly made from 

 Laminaria digitata, Himanthalia lorea, and 

 Scytosiphon filum. 

 4. Family. — Joint-worts (Confervacese). Bodies 

 vesicular, filamentary, or membranous ; co- 

 lour usually green ; cells solitary or many, 

 variously shaped and disposed ; reproduction 

 by zoospores generated in the interior, at the 

 expense of the green matter. Universally 

 found, generally in fresh-, but occasionally in 

 salt-water, also in mud, on rocks, or parasitic. 

 Some occur in such numbers as to colour the 

 waters they inhabit, as Trichodesmium ery- 

 thrceum in. the Red Sea, or Oscillatoria ceru- 

 gescens, which gives a green tint to Glaslough 



