58 



happens Ihal Iho air in Ihe foresl oflen contains more carbon 

 dioxide than in Ihe open lield. The curves in lig. 2 Iherefore give 

 Ihe ioNver Hmil. They indicate Ihat under the CO^ condilions of 

 Ihe sun-planls Ihe shade-planls are decidedly inferior lo these. 



In order to gain information about the conditions of light in the 

 habitats I have made a number of measurements. The plants 

 experimented upon cover in magnificent profusion the drier portions 

 of two fair-sized alder-l)ogs on Hallands Väderö — »Kapellhamn 

 liog» and »Ulagap Bog». In the absence of direct sunlight very 

 low light-intensilies prevail here. In August, at 9, 30 a. m., the 

 light on a Polijslichum-Circea-Oxalis-associMion under a slightly 

 clouded sky was found to be only ./g. Specimens of O.valis under 

 ferns had only gl^ light- As soon as the sun broke out, inten- 

 sities of ?5 could be measured in the direclly illuminated patches'. 

 In an alder-wood, and slill more in a beech-wood, however, the 

 sun-patches are small and therefore soon slip to one side. 



In a Stellaria neinoriim-Oxalis-associaiion under a deeply shading 

 beech-tree Ihe following intensities were measured in succession 

 from 2 to .'} p. m. on a sunny day at the end of June: — 7^5, -^r,, 

 tV» 4^3- ^^y ^y''^ P' "1- the inlensity had fallen to f Ig. Here there- 

 fore the carbohydrate production of the plants should probably be 

 referred to the few hours in the middle of the day, when they are 

 under slronger light. In a lighter part of the wood, under oaks, 

 the following intensities were measured in sunny weather (July 7, 

 12 noon — 3 p. m.): — j-|t, I, t^ö, tV. t. h h h ir- The vegetation 

 here consisls of linbus idaeiis. 



It is generally kiiown that the light in the forest is more in- 

 lense in spring, before the leaves are fully out, and in aulumn, 

 when they are falling (see IIesselman 1904. Wiesner 1907). For the 

 plants here examined however — ^vith the exception of Oxalis — 

 this fact is of no imporlance, since they run Ihrough practically 

 their whole development during the summer. — On Oct. 3 I 

 measured the light intensity in sunny weather at 12 o'clock noon 

 in >.^ Ulagap Bog» and found in one of the darker places vj^j — jV, 

 in a lighter place yV The maximum light of heaven has at this 

 time of Ihe year gone down to \. 



The above ligures may cerlainly give an approximale idea of 



' Since, ac(ordiD<,' to Dorno (Utlft , the direct .sunligbt has a relatively weaker 

 effect upon photographic paper than the diffuse light of heaven, these valnes are 

 probably too low. 



