On Uniformity of Experimental Material 



JACK MYERS, Department of Zoology, University of Texas, Austin, 



Texas 



In the use of algae such as Chlorella and Scenedesmus as experi- 

 mental material, uniformity has two aspects: reproducibility and 

 homogeneity. Reproducible photosynthetic behavior, as observed 

 within a short time span, is readily obtained from replicate aliquots 

 of a harvested suspension. However, harvests taken at different times 

 from a batch culture are known to show wide variability in photo- 

 synthetic characteristics. With increasing density of a culture the 

 average light intensity per cell continually decreases. Light intensity 

 and all other conditions which are functions of cell concentration may 

 be controlled and stabilized by use of steady-state culture devices 

 which maintain cell concentration constant by controlled or con- 

 tinuous dilution. Our continuous-culture apparatus employs a photo- 

 metric system to dilute a culture as fast as it grows and hold constant 

 the cell concentration (1). Both in theory and in practice it yields 

 reproducible experimental material day after day. Its operation is 

 stable except under limitation of growth by a nutrient deficiency in 

 the diluting medium. An inverted kind of steady-state device is the 

 chemostat of Novick and Szilard (2) which employs a constant dilu- 

 tion rate; here operation is stable only if some medium component 

 limits the growth rate. It might be useful for producing algae with a 

 constant nutrient deficiency although it would be sluggish in reach- 

 ing steady-state operation because of the rather low growth rates of 

 most algae. 



Use of steady-state devices such as the continuous-culture ap- 

 paratus yields harvests in which there is a constant frequency dis- 

 tribution of cells at the different stages of their life cycle. The cells 

 are not homogeneous with respect to "age" and may not be homogene- 

 ous in photosynthetic characteristics. That this is indeed the case 

 has been shown by Pirson and co-workers for Hydrodictyon (this 

 symposium), by Tamiya and co-workers for Chlorella ellipsoidea (3) 



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