THE PRODUCTS OF METABOLISM IO3 



material isolated being L-pyrrolidonoyl-a-glutaminyl-L- 

 glutamine:^^ 



CO CO.NH2 CO.NH2 



CH2 CH2 CH2 



I I.I 



CH2 CH2 CH2 



I I I 



NH— CH— CO— NH— CH— CO— NH— CH— COOH 



It appears possible that the pyrrolidonoyl ring may have 

 been formed after extraction of the substance and that in the 

 living alga there is present tri-L-glutamine.^^ 



Other nitrogenous products of algae have received little 

 attention. From their staining reactions it is evident that 

 algal cells contain nucleic acids but only for Polytomella 

 caeca, in which the proportion of ribonucleic acid to protein 

 is as high as 6 to 10 per cent in actively growing cells,^^^ 

 do quantitative investigations appear to have been made. 

 Cyanophycin, a conspicuous reserve product of the Myxo- 

 phyceae, is generally stated to be proteinaceous^'^^ but has 

 not yet been examined in anything more than a superficial 

 manner. 



THE BIOCHEMICAL CLASSIFICATION OF THE ALGAE 



Many, but not all, of the chemical components of algae 

 are characteristic of classes rather than of individual species 

 and the existence of biochemical peculiarities confirms to 

 a remarkable extent the classification derived on morpho- 

 logical grounds.^^^' ^°^' ^^^ The photosynthetic pigments, in 

 particular, are of great taxonomic value, often affording the 

 simplest and most certain means of recognizing represent- 

 atives of different classes (see Table 2). The regular occur- 

 rence of its characteristic pigments in different species 

 belonging to a given class has been confirmed in several 

 investigations.^^' ^'^^ Ahhough the Chlorophyceae has been 

 found to show greater variation in pigmentation than has 

 generally been supposed, the variation occurs between 

 orders and closely related species contain the same pig- 

 ments. ^"^ 

 8 



