igo ALG^ 



&c. The wholeof the marine vegetation of the globe, with the excep- 

 tion of a very small number of species of Flowering Plants, belongs 

 either to the Algse or to the chlorophyllous Protophytes. They vary in 

 size from the microscopic Desmidieae and Pediastrese to that of shrubs 

 or trees in the case especially of some genera of Laminariacese and 

 Fucacese ; and in these classes, as well as in the Florideas, we find a 

 rudimentary differentiation, not only of tissues, but of organs, which 

 leads the way to the much more complete development in the higher 

 classes of the vegetable kingdom. Fresh-water Algae are, with very few 

 exceptions (species of Bangia, Hildenbrandtia, Lithoderma, Hydrurus, 

 &c.), green. Among marine Algse there are many genera of green sea- 

 weeds, belonging chiefly to the families Confervacese, Siphonocladaceae, 

 and Ulvaceas ; but these mostly grow in shallow water. As regards all 

 organisms growing in deep seas, it appears to be essential to them that 

 the green colour of the chorophyll should be masked by a coloured 

 pigment, red in the case of the Florideae, brown in those of the 

 Phseosporeae and Fucacege ; the nature of these pigments will be dis- 

 cussed under the separate families. A few of the smaller species, 

 belonging to the Coleochaetacese, Chordariaceas, and Squamariacese, 

 grow attached to stones, larger Algae, or other marine objects, as fiat 

 •discs, gelatinous cushions, or calcareous incrustations, and the deposition 

 ■of lime takes place to a much larger extent in the corallines. The propor- 

 tion of ash to the organic constituents is much larger in marine than in 

 land or fresh-water plants, seaweeds having the power of extracting from 

 the salt water large quantities of the soluble salts contained in it. The 

 larger species of Fucaceae and Laminariacese are largely used in the 

 north of Europe for manuring the land and for foddering cattle ; and in 

 former times the manufacture from their ashes of kelp and barilla was 

 an important industry. They are also an important commercial source 

 of iodine. From the quantity of gelatine contained in their thallus, 

 some species of Ulvacese, Porphyracese, Fucacese, and Laminariacese are 

 also occasionally used as articles of food or for medicinal purposes. 



Literature. 



Greville — Algse, in Scottish Ciyptogamic Flora, 1823^28 ; Algje Britannicse, 1830. 

 KUtzing— Phycologia generalis, 1843 ; Tabulie Phycologics, 1845-69 ; and Species 



Algarum, 1849. 

 Harvey — Phycologia Britannica, 1846-51 ; Nereis Australis, 1847-49 ; British Marine 



AlgEB, 1849; Nereis Eoreali-Americana, 1851-58; Phycologia Australica, 1858-63. 

 Hassall — British l resh- water Algie, 1 845. 

 Nageli — Die neuern Algensysteme, 1847. 

 Agardh— Species,. Genera, et Ordines Algarum, 1848-80 ; Till Algernes Systematik, 



1872-87. 

 Thuret — Antheridies des Cryptogames, 1851 ; Zoospores des Algues, 1851 ; and 



Etudes Phycologiques, 1878. 



