Assuming Ihat during half Ihe Iwenly-four houis Ihc sliade- 

 planls are not able to assimilate to any approcialjlc exlenl, O.valis 

 Acetosella, for example, will lose every 24 liours ahoiil 12x0.3 = 

 3.6 mg. COg per ÖO cm.- al 18^ In order Ihat a real halance may 

 be reached this loss must J)e made up during Ihr day, whicli, wilh 

 a C()2 percentage of O.s.t mg. per litre and at IS", lakes place 

 at an average lightinlensity of ,,'.j, and lliis Ihcrerorc denolcs tlic 

 absolute point of ecjuilibrium. 



If to this be added the loss in respiration Ihrough nonassimilaling 

 parts (root-syslem, leaf-stalks, etc.) and the necessary increase of the 

 dry weight for growlh and propagalion, it will be seen Ihal the shade- 

 plants must in reality have access lo not inconsiderably grealer ((uan- 

 tities of light than 7,^^, and hence it is easy lo understand the impor- 

 tance of the palches of direcl sunlight in the foresl (cp. p. 58). 



Assuming for the sun-illuminated palches an average intensily 

 of about i, which should probably agree prelty nearly wilh ihe 

 reality, the intensily of assimilation for Siellaria wilh a supply 

 of CO2 of 0.83 mg. per lilre of air proved to be about l.s mg., and for 

 Oxalis about 2. c mg., per öO cm.- for 1 hour at 18'' C. From Ihese 

 figures it can be calculated how greal is the increase per cent in the 

 dry weight of the leaf, when it is illuminated by direct sunlight. 



In an Oxalis plant with a leaf-surface of 50 square cenlimelres 

 I found the dry weight to be 252 mg. (including leafslalks and 

 rhizomes). If the length of the period of assimilation is laken lo 

 be 4^ months, there will Iherefore be required for the building 

 up of this plant an excess of about 2 mg. dry subslance per day. 

 During 1 hours illumination with direct sunlight the increase in 

 weight, calculated as carbohydrale, reaches l.s mg. The respira- 

 tion of the non-assimilating parts should also be taken inlo con- 

 sideration. We Iherefore find that little more than one hours 

 direct illumination of an Oxalis plant is suflicient to maintain the 

 most necessary growlh, even if the light-intensity during Ihc olher 

 hours of the day is only r,^^ (cp. above). 



In Melandriiim the dry weight of the leaves per 50 cm.- surlace 

 is about l.G times greater than in Oxalis. The neod of lighl nuisl 

 therefore be greater. 



The nearer to the soil the forest-plants grow, the higher will 

 be the CO.3 concentration at their disposal. Oxalis, which is one 

 of Ihe most pronounced of shade-plants, bas all ils leaves at bul 

 a little distance from Ihe ground which it covers like a carpet vlig. 7). 



