1, 1920) Ihe sun was shining and a light breezo was hlowing. 

 These eslimations are of course loo few to adinil of our oblainiiifi 

 from them any certain idea of tlie COj percenlage iii Ihe upper 

 regions of Ihe forest. But a priori it seems likely llial Ihe CO., 

 percenlage falls as Ihe distance from the groiind iiicrcascs, and 

 Ihat al the tree-tops during intensive assimilation, in still weather. 

 it may be supposed to fall below the normal. The tigures given 

 also support this assumption. 



In more extensively wooded districts the carbon dioxide produccd 

 from the ground must in ils dilTusion pass the tree-tops too, and 

 doubtless constitutes a not inconsiderable surplus lo Iheir need of 

 CO2. That only a part of the carbon dioxide of the ground reniains 

 in the vegetation was shown above by a comparison of Ihe rarbon 

 dioxide produced and absorbed on equal surfaces in the unit of 

 time. It ma}' also be understood from the circumstance that the 

 air 1 ^ — 2 m. above the ground shows a relatively high percentage 

 of CO.,. The CO 2 production of the ground ought not therefore 

 to be a matter of indilTerence for the growth and increase of the 

 Irees. A closer investigation of the division of the CO., concentra- 

 tion in the dilTerent strata of the air in the foiest ought to yield 

 imporlant results for forestry. 



In the open lield also the CO., concentration in the stratum of 

 air nearest the ground is greater than higher up. Wollnv iFor- 

 schungen aus dem Gebiet d. Agrikulturphysik, Vol. VIII, p. 412), 

 found in a clover-field O.033 % CO2 O.02 m. above the ground, and 

 0.025% 2 m. above the ground. The CO2 concentration on the 

 ground rises after manuring with natural manure (Bt)HNKM.\NN 1920. 

 pp. 48 fl".). But since the wind sweeps över the (ield much m(»re 

 easily than through the forest, the meadow-plants must on tlu' 

 average lie under considerably lower CO^ concentration than tlu' 

 forest-plants, even apart from the fact that less CO., is produced 

 on the ground in the meadow. From the experiments of Wollnv 

 and others it would seem to foUow that the planls in ihe open 

 country even lie partly under abnormal low conditions in regard 

 to the percentage of CO2. This may lead to a real shortage of 

 COo, more particularly in large träets of country covered with 

 vegetation, and this is also proved by the fact that the CO._. per- 

 cenlage över the sea is in the day-time somewhat greater than över 

 the land. 



One conclusion among others that may be drawu is Ihat the air 



