average of 10 eslimalions I obtained O.h.h mg., Avhich is 41 :?ö above 

 the normal. Since nearly all the values \veie laken in the day-lime 

 under full sun, they represen! amounts which really sland at the 

 disposal of the assimilaling vegetation. 



The great variations are naturaily associaled wilh air-currents. 

 The estimations were carried out in the day-time \vith a fresh 

 breeze blowing över the Iree-tops. On the ground only light puHs 

 were observed. The minimum value, O.02 mg., was obtained with 

 obviously moving air, the maximum value, l.js mg., when the air 

 Avas almost still. The estimation of Aug. .'il, from 9.45 a. m. to 

 12 noon, when the value O.71 mg. was obtained 2 melres above 

 the ground, shows that the higher CO^ percentage reaches a little 

 way up from the surface of the earth. 



In the literature there are ver}' few slatements as lo the CO.^ per- 

 centage of the air in the förest, The most delailed investigation 

 seems to have been carried out by Ebermayeh (1885). F^rom 84 

 eslimalions on the air of Bavarian forests he obtained the average 

 value of 0.o:;2y volumes per cent. Some of bis values however are 

 almost twice as great. In thick beech-woods Ihe maximum values 

 of O.oöii) and ().05."<; were found. The lowest values, 0,0200% at a 

 minimum, were obtained in pinevvoods, wilh a layer of möss cover- 

 ing the ground. Ebermayer's values therefore agree well wilh my 

 own experience. Since he sucked in the air from a heighl of H 

 — 2 m., Ihe figures indicale that the air at the level of the under- 

 growth must have been considerably above the normal. 



In tropical rainy forests still higher values than the above-men- 

 tioned might be expected. I have been able to find only two 

 estimations in Ihe literature, viz. Ihose by Mc Lean (1919, p. 157), 

 carried out in the tropical forest near Rio de Janeiro. Using 

 Pettenkofer's melhod he found 0..ii- and O.u % COo, more than 

 10 times the normal therefore. 



How matters are in regard lo the CO., percentage higher up in 

 the wood, on a level with the Iree-lops, has not yel been investi- 

 gated. I have only made a couple of eslimalions of air from an 

 oak-tree in Ulagap Bog. In the upper part of the head of the Iree, 

 11.5 m. above the ground, the value O.i? mg. per litre was obtained. 

 The same CO^ percentage was found in the air around the lower 

 side of the Iree-top, 5 -.-ö m. above the ground. A simultaneous 

 estimation from a Stellaria nemonim-associaWon a little distance 

 away ga ve O.g.» mg. per litre. On the occasion in question (July 



