224 SCIENCE PROGRESS 



at 20°C, 235; at 5°C, 62*9; Fontinalis at 20°C, 150; at 

 5°C, 40; Cinclidotus at 2o°C, 400 ; at 5°C. 75. 



No evidence is found for the assumption that respiration 

 is increased by small increases of light intensity. The respira- 

 tion of the plants examined decreases when the plants are 

 placed in the dark, also during the night. Spirogyra forms an 

 exception in so far that the first night after having been 

 placed in the dark chamber its respiration increases. The 

 author considers that this increase of respiration is due to 

 nucleus and cell division which takes place during the night. 



Although the observations recorded in this paper serve to 

 indicate clearly the complexity of the various external and 

 internal conditions, yet little light is shed on the mode of their 

 interaction. 



The question of the relation between carbon assimilation 

 and other cell processes is also dealt with in a paper by G. 

 Karsten, " Uber die Tagesperiode der Kern- und Zellteilungen" 

 (Zeitsch. f. Bot. 10, 1-20, 191 8). The opinion is expressed 

 that light hinders the cell and nuclear division. 



Osterhout and Haas, "Dynamical Aspects of Photosynthesis" 

 (Proc. Nat. Acad. Sci. 4, 85-91, 1918) and "A Simple Method 

 of Measuring Photosynthesis" {Science, 47, 420-22, 191 8), propose 

 a new method for measuring the assimilation of aquatic plants, 

 which they assert is more accurate than those previously in use. 

 The method is essentially a colorimetric one. To the water con- 

 taining the plant tissue a trace of phenolphthalein is added, 

 and the change in hydrogen ion concentration resulting from 

 removal of carbon dioxide by assimilation is followed by 

 comparison with the colour of standard buffer solutions. The 

 experiments were conducted on a number of algae and on 

 Potamogeton, and from their results the authors conclude that 

 the rate of assimilation increases for the first hour or two after 

 exposure to light before becoming constant. The authors 

 put forward two hypotheses which they think will account 

 for this result, both of which involve the assumption that a 

 catalyst is produced under the influence of light. The dis- 

 cussion of these authors' experiments and conclusions would 

 be premature before more details are available, but it would 

 appear that they under-estimate possible disturbing influences 

 in their experiments. 



A much-needed development of the quantitative measure- 



