6(5 



5, The natural CO,, concentration. 



The results given in Ihe preceding seclion acquire Iheir ecological 

 importance only when Ihe nalural COg percenlage of the air is 

 known. A verv exlensive literature exists dealing wilh the com- 

 posilion of the air. 



Numerous experiments have shown that Ihe CO., concentration 

 över hmd and sea varies Nvithin quite narrow limits, with an average 

 -value of aboul O.os volumes per cent, or about O.55 mg. per litre, 

 calculated at 18" and 760 m/m (see lists in Wollny, Forsch. d. 

 Agricullurphysik, Vol. VIII, p. 407, Letts and Blake 1900, Borne- 

 MANN 1920, p. 4ö, Reinau 1920, pp. 1 ff.). Fr. Schultze (Versuchs- 

 slalionen, Vol. 14, 1871, p. H66) ohtained as average value from 1600 

 analyses O.029 vol. %: Letts and Blake (1900) got the same value 

 from 46 ana lyses. An idea of the breadlh of variation may be 

 oblained e. g. from C. Williams's 142 analyses made in Shetlield 

 (Berl. Ber., Vol. 30, 1897, p. 1451). He oblained as minimum value 

 0.022, and as maximum O.osi vol. %. Brown and Escombe (Proc. 

 Royal Soc, 76 B, 1905, p. 118) oblained from 91 analyses, carried 

 out in the course of 4 years at Kew, a minimum of 2.43, and a 

 maximum of 3.t;o vol. % CO.,. 



Some idea of the variation of the COg percentage by the sea may 

 be formed from my 83 estimations carried out from June to Sep- 

 tember, 19 JO. 



The variation of the C3, percentage from June to September 1920 at the 



Ecological Station, 



CO2 in mg. per lilre air 



40 45 50 55 CO 65 70 75 80 



Nurabers of variants 



The cause of the variations in the composition of the sea-air on 

 Hallands Väderö is probably associated to some exlent with the 

 "svinds. In general it lias been found that in the day-lime land- 

 breezes conlain a lillle less CO2 Ihan sea breezes: at night Ihe 

 opposile is tlie case. My ligures point to a confirmation of tliis 

 theory, allhougli the material is slill too small to admit of more 

 delinite conclusions. A comparison of the lilerature in Letts and 

 Blake (1900, p. 182) shows a surplus value in the night-lime of 

 2 — 14 % över the land. Other factors affecting the COg percenlage 



