94 



DOMESTIC BOTANY. 



water, on the surface of moist stones, or other bodies, some- 

 times like slime, or in jelly-like masses. Above 350 species 

 are enumerated and arranged under about 50 genera. Purple 

 laver {Porphjra vulgaris and P. laciniata), green laver 

 ( Ulva latissima and U. compressa)^ are broad riband-like 

 plants, found on many parts of the rocky coasts of this country. 

 They are used as condiments. 



Star j elly {Nostoc commune). A gelatinous substance spring- 

 ing up in round patches after rain. Nostoc edule is whole- 

 some, and in China is dried, and used in making soups. 



In 1855 several square miles in the Bombay Presidency 

 were covered with Nostoc collinum. The natives called it 

 meat, and considered that it fell from heaven. The spores 

 are supposed to float in the air, and alighting on congenial 

 surfaces where the temperature, and moisture are favourable, 

 spring suddenly into existence, as the perfect plant. 



Several species of ConfervcB are extremely troublesome in 

 ornamental ponds, lakes, and plant aquariums, covering the 

 surface with a foetid scum, or flannel-like masses. 



Ball Conferva (^Conferva cegropila). A native of lakes in 

 many parts of Europe. It is in the form of a ball, of a green 

 colour, and when full grown is about three to four inches in 

 diameter, being composed of successive growths of entangled 

 filaments forming a firm spherical mass. 



The different species of Scytonema, although microscopic 

 in their character, nevertheless, from the great extent of 

 surface they occupy, and their different colours of red, green, 

 and black, form conspicuous objects in nature. 



In Angola (West Africa), the mountain rocks during the 

 rainy season become striped, and ultimately covered as with 

 a black mantle ; this singular appearance being due to the 

 rapid growth of Scytonema chorographicum. In the dry 

 season it peels off like paper, and the rocks assume their 

 natural grey tint. In this country during summer, water in 

 stagnant ponds becomes of a green colour, which is caused 

 by a microscopic globular alga that increases rapidly, and 

 floats in clusters of such density as to give the water the 



