480 SMITH 



have such large central vacuoles that the cell sap may be sampled without 

 difficulty. Chlorophyceae are the most suitable algae for the study of photo- 

 synthesis because their pigments are identical with those of land plants. The 

 Chlorophyceae best adapted for such studies are those in which clones can 

 be maintained in vitro for indefinite periods and which can be grown in pure 

 culture free from all contaminants. For these reasons Spirogyra is unsuitable 

 for most studies on photosynthesis, whereas Chlorella and Scenedesmus are 

 admirably suitable. During recent years many of the fundamental advances 

 in our knowledge of photosynthesis have been obtained through experiments 

 with Chlorella and Scenedesmus. Additional information on photosynthesis 

 has been obtained through study of Phaeophyceae and Rhodophyceae, algae 

 which contain photosynthetic pigments not found in green plants. 



Phycologists are frequently asked the question, of what use to man are 

 algae? This question is usually asked by people familiar with the luxuriant 

 growth of seaweeds along the seashore, who think of them as an untapped 

 source of plant products. One can point out that they are used to a certain 

 extent. Thus they are the source of such gels as alginates and agar. Marine 

 algae are also used as food to a limited extent by Japanese and Chinese. For 

 a number of years the British Government has supported an extensive re- 

 search program seeking additional products of commercial value that can 

 be obtained from seaweeds. Support of the project was to be terminated in 

 1957 because no promising leads had been found. 



With the population of the world increasing at the present rate there will 

 come a time when the available agricultural land will no longer be able to 

 supply food in adequate amounts, despite improvement in agricultural prac- 

 tices and development of better-yielding crops through the efforts of geneti- 

 cists. Even today there are regions in the world where the population is 

 much larger than can be supported by the available acreage of arable land. 

 For this reason there has been widespread popular interest in the proposal 

 that fresh-water algae be cultivated as a supplemental source of food for man 

 and domestic animals. 



Studies on mass cultivation of algae have been made in several laboratories, 

 notably in the laboratory of the Department of Plant Biology of the Carnegie 

 Institution of Washington. Almost all such studies have been with Chlorella 

 pyrenoidosa. Preliminary studies on mass culture of this alga have been 

 in vitro in the laboratory. Spoehr and Milner (1949) have shown that it 

 may be cultured in such a manner that there is either a high fat or a high 

 protein content. When cultured so that there is a high protein content it 

 may comprise more than 50 per cent of the dry weight. Computations by 

 Spoehr (1951) based upon culture in vitro in the laboratory estimate that 

 there might be a yield of 40 tons of dry high-protein material per year per 

 acre. This is a much higher yield of protein per acre than is known for any 

 agricultural crop. 



