70 



it. Neverlheless even here il is probably Ihe toprnosl leaves Ihal 

 lake över Ihe grealer part of Ihe assimilalive work, for Ihe lighl 

 which has already passed lhrouj;h a leaf is deprived of praclically 

 all ils assimilaling posver (see Willstätter and Stoll 1918, p. 

 127). The lower leaves are therefore Ihrown back upon Ihe 

 quantilies of light Ihat filler between Ihe leaves above Ihem- 

 Accordingly il is probably lo be assumed Ihat in shade-planls the 

 really assimilaling surface is seldom greater Ihan Ihe surface of 

 Ihe ground benealh Ihe plant. 



The comparisons made above belween Ihe carbon dioxide pro- 

 duced by Ihe ground and Ihal consumed again by the covering 

 of vegetation ought Iherefore lo appl\' quile generally for more 

 Ihickly-leaved \voods. And if it is remembered Ihat il is only 

 during Ihe lighter hours of Ihe day that Ihe assimilation reaches 

 Ihe same values as Ihe CO2 production, whereas Ihe latler process 

 goes on day and night \vilh about Ihe same inlensily, \ve come 

 lo Ihe conclusion Ihal the lotal CO2 produclion from Ihe ground 

 considerably exceeds Ihe consumplion of CO2 in Ihe assimilalory 

 work of Ihe herbaceous vegetation. This agrees well wilh Ihe facl 

 thal wooded ground gets mosl of ils carbon not from rotled remains 

 of Ihe undergrowlh hut from the fallen leaves of Ihe Irees. Even 

 if all the carbon does not pass back in the form of carbon dioxide 

 of decomposilion, bul part of it slays in Ihe ground, Ihe foiiage 

 of the Irees is neverlheless so extensive in relation to the suiface 

 of the ground Ihal Ihere must be an excess över the undergrowlh. 



All the carbon dioxide liberaled from the ground will nalurally 

 not be available for the vegetation, on accounl of dilTusion, and 

 above all the v^ind. But thal the carbon dioxide of the ground 

 none the less considerably contribules lo raise the CO2 percentage 

 in the lower slrata of the air in the forest will appear from the 

 following analyses of air, which I carried oul both wilh my own 

 melhod and wilh the aspirator melhod (K) lilres of air in the 

 course of 2 — 3 hours). See the following page. 



The figures show thal the COg percentage of the air in the 

 förest varies very greally, but is as a rule considerably higher than 

 the CO2 percentage in the air över the open field. The average 

 for the latler during August was O.cis mg. per lilre (p. 52). The 

 air of the forest at the level of Ihe undergrowlh shows during the 

 same period a minimum value of O (527 mg. and a maximum of 

 1.2.'i4 mg. per litre. which is more than Iwice the normal. As an 



