— 244 — 



Loss of dry matter: Respiration. 



Leaves 24 X 0.8 == 19 mg 



Stem + root 24 X 0.96 X 0.16 = 4 - 



23 mg C0 2 = 14 mg dry matter. 



The production of dry matter per 50 cm 2 per day = 60 — 14 = 46 mg === 

 16.5 °/o of the dry matter of the plant. 



In a similar manner it will be possible to calculate the percent 

 production of dry matter also for the other months of the year, 

 when the intensities of light are known. 



3b. Percent production of matter, directly estimated. 

 It was mentioned above (page 235) that the percent production can 

 also be estimated directly, but only when the whole, or at any rate 

 a constant part of the new built organic matter is used in forming 

 leaves, so that the production of matter is always proportional to 

 the dry matter of the plant (which is not the case when flowering 

 begins). The experiments were carried out in such a way that plants 

 of Sinapis alba were grown in a flower pot until 2 — 4 leaves had 

 appeared, when the dry matter of the plants was estimated. The 

 vegetation time was reckoned from the time when the cotyledons 

 expanded (about 8 days after the sowing of the seeds) until the 

 termination of the experiment. The percent production of matter 

 was calculated after the method given on page 236. The result of 

 the experiments was as follows: 



20 



Dec. Jan. Febr. March Apr// May June 

 Fig. 5. Percent production of dry matter in Sinapis alba. 



