STUDIES OF SPORE-PLANTS 251 



241. Brown and Red Algae. These are chiefly marine 

 plants, and are commonly known as sea-weeds. Numerous 

 kinds of these may be seen on any sea-shore. The red and 

 brown colors appear to be due to pigments which conceal 

 the chlorophyll. At any rate these plants make their own 

 carbohydrate foods from carbon dioxide and water just as 

 higher green plants do. Studies of the structure and life- 

 histories of these interesting algae must be left for college 

 courses of botany. 



242. Economic Relations of Algae. Probably the great- 

 est value of the algae lies in the fact that they make food for 

 higher organisms. This may be observed in any aquarium 

 where snails rasp off and eat the green algae on the glass. 

 Numerous small animals eat algae, and these animals may 

 serve as food for still larger animals. Immense quantities of 

 these low plants are found in the ocean down as far as light 

 penetrates. Even some large animals, e.g., certain fishes 

 and whales, have strainers in their mouths which enable them 

 to collect large quantities of very small organisms, some of 

 them animals and some plants ; but especially do small ani- 

 mals which feed on simple algae serve as food for the larger 

 animals. It is now quite certain that directly or indirectly 

 the simplest green plants play an important part in the food- 

 supply of aquatic animal life, much of which is of use to man. 

 In this line the simple algae have great economic importance. 



Many kinds of the larger sea-weeds have some economic 

 uses. Thus iodine is prepared from the ash obtained by 

 burning sea-weeds, and formerly this was also the chief source 

 of sodium carbonate, from which baking soda is made. Cer- 

 tain brown sea-weeds are used as food by Chinese and 

 Japanese and by the natives of the Malay Archipelago. 

 Agar-agar and Irish moss, both used in preparation of jellies, 

 are made from certain kinds of sea-weeds. Finally, in some 

 agricultural countries near the sea the sea-weeds cast up by 

 the waves are used as soil fertilizers. 



