SOME BOTANICAL FACTS ABOUT ALG^E 27 



The stem-like forms of certain algas are composed of cylindrical 

 cells which combine or grow in a longitudinal direction chiefly. 

 Sometimes the cells are arranged evenly, in which case the stem 

 seems articulated, as in some species of Ceramium. Again, they 

 are irregularly placed, so that the stem appears solid. 



The highest types of algae in the differentiation of parts, or 

 vegetative forms, are to be found in the Fucacece, of the brown 

 seaweeds; the highest in the reproductive development, in the 

 red class. 



Reproduction by cell-division, in which the organism itself 

 breaks up into two or more individuals, is called vegetative repro- 

 duction. Higher forms reproduce by spores, or germ-cells, which 

 give rise to new individuals on germination. 



The substance of an alga is more or less firm, according as the 

 vegetable mucus or gelatinous matter it contains has more or less 

 consistency; it is membranaceous when the gelatine is scant and 

 glossy, gelatinous when it is abundant and fluid, and cartilaginous 

 when it is hard. 



Some algae are annuals ; a few are perennials, and cast off and 

 renew their laminae every season. Many plants present quite a 

 different appearance at different seasons of the year, and so are 

 often difficult to identify. Those which form spores throw off 

 these isolated cells, which sink or are washed to positions where 

 they germinate and begin their cycle of life. Many of the spores 

 begin their growth at once, without regard to season, so the 

 species is ever present. 



