INTRODUCTION 3 



lipide constituents of algae developed. Particularly note- 

 worthy series of papers on algal chemistry have been pro- 

 duced by Haas, Colin, Heilbron and Percival and their 

 respective collaborators (see references). 



A second type of investigation has been concerned with 

 the growth of algae in culture. Microscopic algae were not 

 neglected by the microbiologists following Pasteur but pro- 

 gress in their investigation w^as slow in comparison with 

 that in other branches of microbiology, probably because 

 of the greater technical difficulties in culture and manipula- 

 tion. Many studies were made with cultures which were 

 not absolutely pure and work of this type, for example that 

 of Molisch published in 1896,^^^ showed the mineral re- 

 quirements of simple algae to be much the same as those of 

 higher plants. Further reliable work on nutrition could only 

 be carried out with pure cultures. Beijerinck in 1890 first 

 described the isolation, in what was probably pure culture, 

 of Chlorella vulgaris and similar unicellular green algae by 

 means of the methods developed by Koch for bacteria. ^^ 

 Subsequently other techniques appropriate to particular 

 kinds of algae were worked out but these need not be 

 particularized since the history of algal culture techniques 

 has been summarized by Pringsheim,^^^ himself a dis- 

 tinguished w^orker in this field. By 1920 many species had 

 been isolated in a bacteria-free state and investigations 

 under controlled conditions were undertaken. At first quali- 

 tative studies of nutritional requirements (see ref. 132, for 

 example) predominated. Precise quantitative methods for 

 the investigation of the growth of simple algae were intro- 

 duced by Bristol Roach in 1926^^^ in a study of the effects of 

 carbon compounds on soil algae. Such work has established 

 the main features of the growth in culture and the major 

 nutritional requirements of those algae which are most 

 easily grown under laboratory conditions. More direct 

 studies on the metabolism of algae in culture were begun 

 by Pearsall and Loose, who in 1937^^^ showed that the main 

 trends of the chemical changes occurring during the growth 

 of a Chlorella population are similar to those occurring 

 during the development of a leaf of a higher plant. 



