The Algae loi 



THE ALGAE 



It is a vast assemblage of plants that makes up this 

 group; and they are wonderfully diverse. Most of 

 them are of microscopic size, and few of even the larger 

 ones intrude upon our notice. Notwithstanding their 

 elegance of form, their beauty of coloration and their 

 great importance in the economy of water life, few of 

 them are well known. However, certain mass effects 

 produced by algae are more or less familiar. Massed 

 together in inconceivably vast numbers upon the sur- 

 face of still water, their microscopic hosts compose the 

 ' 'water bloom. ' ' Floating free beneath the surface they 

 give to the water tints of emerald* of amberf or of 

 blood t. ]\Iatted masses of slender green filaments 

 compose the growths that float on oxygen bubbles to 

 the surface in the spring as "pond scums." Lesser 

 masses of delicately branched filaments fringe the 

 rocky ledges in the path of the cataract, or encircle sub- 

 merged sticks and piling in still waters. Mixtures of 

 various gelatinous algae coat the flat rocks in clear 

 streams, making them green and slippery; and a rich 

 amber-tinted layer of diatom ooze often overspreads the 

 stream bed in clear waters. 



These are all mass effects. To know the plants com- 

 posing the masses one must seek them out and study 

 them with the microscope. Among all the hosts of 

 fresh water algae, only a few of the stoneworts (Char- 

 aceae) are in form and size comparable with the higher 

 plants. 



Many algae are unicellular; more are loose aggre- 

 gates of cells functioning independently; a few are 

 well integrated bodies of mutually dependent cells. 



* Vol vox in autumn in waters over submerged meadows of water weed. 



fDinobryon in spring in shallow ponds. 



%Trichodesmium erythrcBiim gives to the Red Sea the tint to which its 

 name is due. The little crustacean, Diaptomus, often gives a reddish tint to 

 woodland pools. 



