SUMMARY AND CONCLUSIONS I33 



enzymes responsible for the synthesis of specific meta- 

 boHtes leads to the appearance of nutritionally exacting 

 forms similar to those well known among bacteria, fungi and 

 other organisms. A few algae, both naturally occurring 

 strains and artificially induced mutants, have been shown 

 to have a requirement for thiamine and it seems likely that 

 when a more thorough investigation is made, the growth of 

 many algae will be found to be dependent on the exogenous 

 supply of specific organic factors. Such growth factor re- 

 quirements occur quite independently of the presence or 

 absence of a capacity for photosynthesis. 



Many of the algal classes are characterized by the general 

 occurrence in their members of particular metabolic pro- 

 ducts. This is especially evident with the photosynthetic 

 pigments, each class having its distinctive accessory pig- 

 ments. Peculiarities in carbohydrate metabolism occur in 

 several classes. The Phaeophyceae and Rhodophyceae, for 

 example, tend to produce carbohydrates containing i : 3 

 linkages, rather than i : 4 linkages such as are formed by 

 other algae and higher plants, and polysaccharide sulphate 

 esters. Those algae grouped together in the Chrysophyta 

 seem unable to synthesize starch and generally accumu- 

 late fat rather than carbohydrate reserves. The occurrence 

 of these and other biochemical characteristics confirms to 

 a remarkable degree the classification of algae derived on 

 morphological grounds. 



Its possession of such features justifies the consideration 

 of the algal type of metabolism as a distinct field of study 

 which has much to contribute to comparative biochemistry 

 and our understanding of the economy of nature. 



