12 



tables, we will also mention the number of cM^. N/lOO 

 NaoSoOa necessary for the titration. 



It may incidentally be remarked hère that the method of 

 Winkler is also applied by K n i e p *) for the investiga- 

 tion of the CO^-assimilation. This investigator covered 

 the water, in which the assimilating Helodea-shoots were 

 put, with a layer of olive-oil. Apart from the circumstance 

 that this method of arranging the experiments did not 

 suit our purpose, it may be noticed hère that some expe- 

 riments done in the „Laboratory for microscopical anatomy" 

 showed that this way of shutting ofï the oxygen is very 

 imperfect. In fact in this way the oxygen of the air 

 permeates as quickly into the water as when the water is 

 directly in connection with the air. 



e. Calculation of the average velocity of assimilation. 



The quantity of oxygen présent in the flasks having 

 once been fixed, by means of thèse data and by taking 

 into account the capacity of the flasks, the quantity of 

 oxygen which would be présent in 350 cM'\ water of 

 the same concentration of O^ can be immediately calculated. 



We expressed the amount of oxygen by the équivalent 

 quantities of N/lOO NaoSoO.; 1 cM^ N/lOO Na.S.Os 

 being équivalent to 0.08 mgr. Oo. 



Taking this quantity of NaSoOa-solution necessary for 

 the original water to be: a^, and that for the water after 

 having flowed along the shootss: a^ and indicating the 

 velocity of the watercurrent by t, viz. the time in minutes 

 necessary for collecting 350 cM''. when the velocity was 

 constant, then the average velocity of assimilation during 

 the period of fiUing the flasks expressed in mgr. oxygen 

 per minute is given by the foUowing formula: 



60 ,. _„ 



f = {a.2 — aj /. U,0o mgr. 



') jahrb. f. Wiss. Bot. 56, PfefFerband. 1915, S. 460. and Handwôrterb 

 d. Naturw. Bd. 7 (1912). S. 701. 



