52 



THE METABOLISM OF ALGAE 



information about the manner in which these substances 

 are utiUzed. More useful comparisons of the effects of 

 different substrates are possible if growth is followed quanti- 

 tatively throughout the development of the cultures. A 

 model for investigations of this sort is that of Bristol 

 Roach^^^' ^^^ in which the effect of a number of organic 

 substances on the growth of Scenedesmus costidatus var. 

 chlorelloides was studied. Under the culture conditions used 

 exponential growth lasted for several days and the relative 

 growth constant (see Fig. 12 and page 107) could be used 

 for the quantitative comparison of growth in the presence 

 of different substances. The results obtained by Bristol 

 Roach are summarized in Table 4. It is to be noted that 

 in a light intensity which was not saturating for photo- 



TABLE 4 



RELATIVE GROWTH CONSTANTS, EXPRESSED AS PERCENTAGES 

 OF THE MAXIMUM, CHARACTERISTIC OF THE GROWTH OF 



Scenedesmus costulatus var. chlorelloides in the presence 



OF VARIOUS SUBSTRATES 



The light intensity used was not saturating for photosynthesis 2^° 



svnthesis both hexoses and disaccharides accelerated growth 

 but that certain substances, particularly the pentose sugar 

 xylose, had an inhibitor^' effect. 



It is generally accepted that the reactions in which the 

 intermediates of metabolism are involved are reversible 

 and that intermediates and enzymes together form a com- 

 plex but flexible system into which material can be intro- 

 duced at many points and through which material flows in 

 a direction determined rather by the conditions to which 

 the organism is exposed than by the nature of the mech- 

 anism itself. Because the respiratory system is intermeshed 

 with other metabolic systems then it would seem that any 

 substance which can serve as a substrate for respiration and 

 so yield energy ought at the same time to be capable of 



