— 235 — 



of respiration of the plants. Care must be taken that only a part 

 of the oxygen in the jars is used by the plants. The plant material 

 must not touch the bottom, so it is fitted either in a bottle of gauze, 

 hanging from the lid, or it is put on a perforated disk of paper or 

 cork, held up from the bottom by needles. 



In the bottom is the absorbing fluid. When the plant material 



is little, y — ^ Baryta solution is to be used ; with more plant mate- 

 rial NaOH solution in greater or less concentration. When a suitable 

 time has elapsed the amount of the G0 2 absorbed is determined 

 by titration. If baryta solution be used the fluid can be titrated 

 directly with HCl; if NaOH solution, the absorbed CO 2 must first 

 be precipitated with BaCl 2 after the method of Sørensen and 

 Andersen (1908 p. 279). 



The absorption of the C0 2 given off by the plants takes places 

 very quickly. 



Example. Leaves of Rumex acetosella, area = 48 cm 2 . 



The leaves were put in a glass jar, vol = 100 cm 3 , in the bottom 



of the jar 1 cm 3 ca. y baryta solution, corresponding to 2.85 cm 5 



The jar with the leaves was placed in darkness for 6 hours 

 at 17°. 



The titration value was then 1.15 cm 3 HCl; the G0 2 given off 

 by the leaves is 2.85 4- 1.15 = 1.7 mg G0 2 : 



Respiration pr. 100 cm 2 pr. hour = 0.59 mg G0 2 . 



4. Estimation of the dry matter. This estimation is made 

 in the usual way by drying the plant material first at 60° until 

 most of the water has evaporated and then at 100° to constant 

 weight. 



5. Direct estimations of the production of matter. 

 From the above mentioned estimations it will be possible to calculate 

 the amount of dry matter produced pr. unit of area pr. 24 hours. 

 In order to check the obtained value it is also possible sometimes 

 to measure directly the production of organic matter. 



In the propagation of diatoms for instance the new diatoms 

 can assimilate G0 2 in the same manner as the parents and the 

 production of organic matter will always be proportional to the 

 amount of diatoms. The reproduction is progressive, if none of the 

 diatoms are destroyed. Supposing that the amount of diatoms is 



16* 



