AGRICULTURAL BOTANY, CHEMISTRY AND PHYSIOLOGY OF PLANTS I755 



denitrification was suspended, but a vety limited sup])ly of oxygen 

 (" niicroaerophily ") favoured the process. Low temperatures of o" to 3° C. 

 did not inhibit denitrification. As a result of his experiments, the writer 

 concludes that denitrification is quite possible in the Arctic Ocean and 

 that Brandt's hypothesis is not confirmed by the facts observed. 



Finall}', arctic waters were shown to contain two kinds of bacteria 

 capable of producing sulphuretted hydrogen, one from sulphates {Mi- 

 cros Hra eastuarii) and the other from organic matter. It is pointed out that 

 the formation of black nmd on the coasts of Murman arid Novaya Zem- 

 bj'a and in Moghilnoie Lake in the Island of Kildine is due to the activity 

 of these bacteria, more especially M. aestiiarii. 



1268 - The Optimum Temperature of a Diastase is Independent of the Concentration 



of Substrate and Enzyme. — Compton a., in Annales dc Vlnstitut Pasteur, VoL XXX, 

 No. 9, pp. 496-502. I'aris, September 1916. 



In a previous investigation (i) it has been shown that the optimum 

 temperature of a salicinase from sweet almonds is independent of the con- 

 centration of the substrate and of the enzyme itself, provided the duration 

 of the enzyme action remain the same. In order to determine whether the 

 statement would hold for enz3'mes in general, a similar series of experi- 

 ments was carried out with the maltase of As-herpillns Oryzae or takadia- 

 stase. Kahlbaum's purified maltose was emplo^^ed and the diastase solu- 

 tion was obtained by macerating i gm. of the diastase powder in 100 cc 

 of ])ure water at room temperature. Then using solutions of hydrolised mal- 

 tose of the following molecular concentrations: M/5, M/io, M/20, M/30, 

 the activity of the enzyme was determined at temperatures varying from 

 170 to 56..4« C. 



To measure the influence of the concentration of the diastase, solu- 

 tions were prepared with o.i, 0.3 and 0.6 gms. of diastase powder per loocc 

 of water as well as the standard solution given above. Again, in all four cases 

 the optimum temperature was 47'' C. 



The writer is of opinion that with diastase fermentations the opti- 

 nmm temperature is always independent of the concentration of the sub- 

 strate and of the enzyme. This fact is of practical importance as it means 

 that the molecular concentration of the substrate solutions is not an im- 

 portant factor and need not be considered when substances such as gly- 

 cogen, starch and proteins are used, whose molecular concentration is 

 often unknown. 



1269 - On the Reduction of Nitrata by Plants with Evolution of Oxygen. — molliardm., 



in Comptcs Rendus des Seances dc V Academic des Sciences, Vol. 163, No. 15, PP- 371-373- 

 Paris, October 9, 1916. 



There are grounds for believing that nitrates are reduced in the leaves 

 of plants and it has been suggested that there might be a resulting 

 evolution of oxygen. An attempt was made to show that such an action 



(i) Arthur Compton, in Proceedins,s of the Royal Society, B. 87, 1914. I'- 24.") ; Annales de 

 Vlnstitut Pasteur, VoL XXVIII, 1914, P. 866. 



