— 221 — 



sities of light and at different temperatures, and a curve indicating 

 the influence of light on the C0 2 assimilation should be con- 

 structed. With the help of this curve and the curve for the 

 variation of light it will be possible to calculate the gain of dry 

 matter from the C0 2 assimilation per 50 cm 2 during a day. 



Expense. Next the respiration of the leaves and the stem 

 and root should be determined per i g and per hour ; from this it 

 will be possible to calculate the loss of dry matter through 

 respiration during a day. 



By subtraction of the loss from the gain, the net amount 

 of dry matter produced during a day can be measured. By 

 calculating it in percent of the dry matter of the plant we find 

 the daily percent production of matter. 



By calculations carried out in this manner it should be possible 

 to gain an insight into the economic working of the plant. For 

 instance such experiments would give information as to the 

 difference which certainly is to be found between the intensities 

 of G0 2 assimilation and respiration in different plants, and as to 

 the significance of these differences for the economy of the plant ; 

 farther they might show a difference between plants with deciduous 

 and those with evergreen leaves, between plants with a great 

 mass of stem, and those without stem, between annual and 

 perennial /plants; in short such investigations may cast light on 

 how the production of matter is regulated in any single case. 



The following experiments are to be considered as a prelimi- 

 nary attempt so solve some of the problems alluded to above. 



2. Methodic. 



1. Estimation of the intensity of C0 2 assimilation. 

 In order to determine the amount of C0 2 which plants in natural 

 conditions assimilate it is necessary during the experiment to keep 

 the plants in conditions resembling natural conditions as much as 

 possible, and before all, the determinations should be carried out 

 in an atmosphere with about the same C0 2 content as the air, 

 viz 0.3 °/oo. Still in most experiments the plants have been enclosed 

 in a flask in an atmosphere with 5 — 10 °/o G0 2 , the tension being 

 determined at the beginning and end of the experiment. Of course 

 experiments made in this manner may give information on many 

 points concerning the C0 2 assimilation; but for determining the 

 amount of C0 2 , assimilated under natural conditions, this method 

 is not fitted, since the intensity of assimilation, as Kreussler and 



