410 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 5 



will be able to carry on its life processes more easily than the other 

 plants and animals. Wherever the curiosity of man has carried 

 him in his travels, this plant group, the algae, truly ubiquitous in 

 comparison with other live forms, is growing — enormous, as the slimy 

 kelps that are washed onto the seashore after a storm, or minute, as 

 the slime covering the ponds, each cell or individual plant of which is 

 so diminutive that it can be made visible only with a high-powered 

 microscope. 



NATURE OF ALGAE 



The simplest forms of plant life, the algae, are thallus plants 

 varying in size from a single microscopic cell as small as one thou- 

 sandth of a millimeter in diameter to a multicellular individual 

 made up of millions of cells and sometimes several hundred feet in 

 length. Algae have no true roots, stems, or leaves like those of the 

 higher plants with which most of us are more familiar. Instead 

 of reproducing themselves by means of seeds, as is customary with 

 the higher plants, these lower plants form new individuals by the 

 division of a single-celled individual into two new single-celled indi- 

 viduals of equal size or by the formation in a cell of the parent plant 

 of spores, which, when released, develop into new plants. The 

 spores may be motile or nonmotile and according to the different 

 species may be produced in number from 4 to 64 or more at a time. 

 The algae, like other plants, possess chlorophyll, or green pigment, 

 and are thus able to make their own food from inorganic materials 

 such as carbon dioxide, water, and certain mineral substances with 

 the aid of light. 



The names of the five classes of algae are based upon the char- 

 acteristic differences in color. These five classes are the green algae, 

 or Chlorophyceae ; the blue-green algae, or Cyanophyceae ; the yellow- 

 green algae, or Chrysophyceae ; the brown algae, or Phaeophyceae ; 

 and the red algae, or Rhodophyceae. The brown and red algae 

 contain chlorophyll, but the green pigment is masked by the other 

 colored pigments associated with it. 



ENVIRONMENTAL FACTORS FOR THE GROWTH OF ALGAE 



The food or elements essential for the growth of the algae are 

 the same as those necessary for the growth of higher plants. Calcium 

 is not essential for many algae, but certain of them are unable to 

 develop in its absence. Calcium, potassium, and magnesium are im- 

 portant because their bicarbonates furnish a supplemental supply of 

 carbon dioxide for photosynthesis, which is the production of sugar 

 from water and carbon dioxide taking place by the action of chloro- 

 phyll in light. During this process, a part of the oxygen is set free. 



