GROWTH AND METABOLISM II3 



carbohydrate or similar compound is the principal product 

 of metabolism. A photosynthetic quotient corresponding to 

 the production of fat only, e.g. Qp for the formation of 

 glycerol tripalmitate = i-42, has apparently never been ob- 

 served in this type of experiment,^^^ but the tendency for 

 the observed values to exceed unity suggests that a small 

 proportion of fat or protein is normally produced. Only one 

 of the values given in Table 10, that for Chlorella sp., differs 

 by a statistically significant amount from the mean value, 

 1-045, of all those given and it is clear that this deviation 

 is not one characteristic of the Chlorophyceae generally. 

 Table 10 shows that representatives of classes having quite 

 different storage products (see Table 9) nevertheless form 

 photosynthetic products of similar composition when ex- 

 posed to similar conditions. This provides further evidence 

 for the view that the mechanism of photosynthesis is funda- 

 mentally the same in all types of algae. 



Nitzschia and Chlorella spp. when deprived of phosphate 

 show a pattern of be haviour similar to that characteristic 

 of nitrogen defi ijency. Carbon assimilation continues in 

 phosphorus-deficient cells and on return to a complete 

 medium there is an enhanced rate of phosphorus uptake. ^^^ 

 Phosphorus-deficient cells of Polytomella caeca have been 

 found to show accelerated protein synthesis immediately 

 following addition of excess of phosphate to the culture. 

 This is accompanied by a decrease in ribonucleic acid con- 

 tent but subsequently there is an increase in ribonucleic 

 acid content the rate of which far exceeds that of protein 

 synthesis. ^^* These e ffects a^re_perh aps t o be interpreted^ a^s 

 the result of inorganir phosphatelBeing immediately avail- 

 able for the energy transfer mechanisms of protein synthesis 

 whereas its incorporation into nucleotides is a slower 

 process. 



In cultures made in a limited volume of medium expo- 

 nential growth of algae sooner or later ceases. The factors 

 bringing this about are various, the following being the more 

 important: (i) Exhaustion of a nutrient substance from the 

 medium; culture media generally contain all essential nutri- 

 ent substances in quantities sufficient for luxuriant growth 



