ALGiE OK HYDEOPHYTA. • 655 



gasmm baceiferum, the Gulf-weed, is found floating iu great quan- 

 tities on each side of the equator in the Atlantic, Pacific, and Indian 

 oceans. Protococcus nwalis and viridie occur in red and green 

 snow. The red and. green colours of certain lakes and seas are 

 attributed to species of Trichodesmium and Sphcerosyc/a. According to 

 Dr. Hooker, Diatomacm are found in countless numbers between the 

 parallels of 60° and 80° S., where they give a colour to the sea, and 

 also to the icebergs floating on it. The death of these bodies in the 

 South Arctic ocean is producing a submarine deposit, consisting entirely 

 of the siliceous particles which entered into the composition of these 

 plants. Conferva crispa, called Water-flanuel, forms beds of entangled 

 filaments on the surface of water. Species of Tyndaridea also occur 

 in thick green patches. Hydrodictyon utriculatum, Water-net, has the 

 appearance of a green net, composed of filaments which' enclose pen- 

 tagonal and hexagonal spaces. Achlya prolifera, and other Saproleg- 

 nieee, are developed occasionally on living animals, such as on the gills 

 of the gold-fish and of trout, as well as on dead flies and other organic 

 matter. Certain organisms have been detected in the human stomach 

 which appear to belong to this order. One of these is called Sarcirmla 

 ventriculi by Goodsir, and was ejected by vomiting in a case of 

 pyrosis. It consists of square cells united together in sets of four, and 

 propagating by division. It is probably an anomalous condition of a 

 mould-fungus. 



The plants of this order supply a quantity of gelatinous matter, 

 and many of them are used for food. Kelp is obtained by the burn- 

 ing of Seaweeds, and iodine is procured from them. Sphcerococcus 

 (Chondrus) crispus, Carrageen or Irish Moss, supplies a nutritious 

 article of diet ; so does S. lichenoides, Ceylon Moss. Bhodymenia pal- 

 maia, Dulse, Alaria esculenta, Iridcea edulis, young plants of Laminaria 

 digitata and saccharina, Tangle, as well as various species of Porphyra, 

 Laver, and Ulva, Green Laver, are esculent. The edible swallows'- 

 nests of the East are said to be formed of a species of Oalidium. 

 Sphcerococcus cartilotginens, var. sstaceus, is used in China as a substi- 

 tute' for these nests^ Agar-agar is a seaweed of a similar kind. 

 JVostoc edule is used in China as an article of food. The use of burnt 

 seaweed, in cases of scrofulous swellings, has been superseded by the 

 discovery of iodine, the active ingredient. Plocaria {Gigartina) Hel- 

 minthocorton, under the name of Corsican Moss, was formerly used as 

 a vermifuge. 



