836 METHODS OF KINETIC MEASUREMENTS CHAP. 25 



steady; while, in a 0.1 M KHCO3 solution, there resulted an increase in 

 rate by about 30% within six hours, followed by several hours of steady 

 oxygen production and then a rapid decline. In a mixture of 0.035 M 

 KHCO3 and 0.065 M NaHCOs, the rate remained unchanged for about 

 fifteen hours, after which the stimulating effect of the potassium salt ap- 

 parently wore off, and the rate declined rapidly (fig. 25.1). In all these 

 experiments, the cells spent about one half of the total time in light and 

 one half in darkness. 



Among other algae used in quantitative photosynthetic studies were the 

 Chlorophyceae: Scenedesinus {cf., for example, Gaffron 1942), Hormidium 

 flaccidum (van der Honert 1930 and van der Paauw 1932), Stichococcus 

 hacillaris (Aufdemgarten 1939); the Rhodophycea, Gigartina harveyana 

 (Emerson and Green 1934) ; the Cyanophycea, Chroococcus (Emerson and 

 Lewis 1942); the brown alga, Fucus serratus (Steemann-Nielsen 1942); 

 and the diatoms, Nitzschia dosterium (Barker 1935, Button and Manning 

 1941), A^. dissipata (Wassink, Kersten 1945), Navicula minima (Tanada 

 1951). 



Advantages of algae as material for photosynthetic measurements (e. g., 

 the convenient use of manometric methods) are shared to some extent by 

 the higher aquatic plants. Among them, Elodea has been the most popular 

 in photosynthetic studies, because of its widespread occurrence in stagnant 

 waters. Other aquatic plants used in photosynthetic work were Cahomba 

 caroliniana (Smith 1937) and Potomageion (Gessner 1937). 



Detached leaves provided the material for most of the earlier investigations 

 of photosynthesis ; they were used by Blackman and co-workers, by Brown 

 and Escombe (1905) and by Willstatter and StoU (1918) in their pioneer 

 investigations of the quantitative aspects of photosynthesis. Because of 

 the interruption of natural translocation processes, the time course of 

 photosynthesis in detached leaves may differ from that in similar leaves 

 attached to the stem (Vol. I, p. 332). 



Whole land plants, enclosed in glass vessels, were long used in investiga- 

 tions of the rate of photosynthesis under field conditions. A group of 

 workers at the Smithsonian Institution in Washington {cf. Hoover, Johns- 

 ton and Brackett 1933 and McAlister 1937) showed that this method can 

 give results equivalent, as to precision and consistency, to those derived 

 from experiments with algae. The material used in their studies were 

 single young wheat plants. 



The culture of purple bacteria that can be used for studies of bacterial 

 photosynthesis has been described by van Niel and co-workers (1931, 

 1944), French (1937), Gaffron (1933-1935) and the Dutch group (Eyniers, 

 Wassink, Katz, Dorrestein et at. 1938, 1942) ; the bacteria used included 

 Rhodospirillvm rubrum, Streptococcus varians, and strains of Chromatium 

 and Rhodovihrio. 



