84 



favouied both in regard to light and to carbon dioxide. Fig. 9 gives 

 an idea of the vegetation of tlie damp seaweed-beds. 



The inlensity of respiration is somewhat greater in Nasturtium 

 than in the forest-plants exain^ned^ In the latler il amounted to 

 ahout 0..( mg., in Naslnrlium it is 0.4? mg. per 50 cm. 2, 18", and 1 hour 

 (average from 4 estimations). This value seems to be somewiiat 

 lower than for olher sun-planls {Helianthus O.7 mg., according to 

 Blackman; cp. Boysen-Jknsen 1918, p. 242j. 



In olher shore-piants I have found much higher respiration- 

 values. Thus Aster Tripoliiim in the heighl of summer at about 

 28" C. brealhes out I.,-) mg. CO2 per 50 cm.^ per hour. The intensily 

 of the respiralion depends upon the condilions of nourishment, and 

 my relalively low values for Naslnrlium may perhaps be due to 

 the fact that the experiment was carried out at the beginning of 

 Oclober, upon plants which had slood under less than normal light. 



On sunny days the shore-plants live under light-intensilies which 

 during the difTeient hours of the day amount to the following values 

 (taken June 25—27, 1920j-: 



3 a. m. 4 a. m. 5 a. m. 7 a. m. 8 a. m. — 4 p. m. 

 9 p. m. 8 p. m. 7 p. m. 5 p. m. \ 



1 111 



-§0 Tö 9 ^ 



Since respiration and assimilation in Nasfuriiiim counterbalance 

 each olher at about ^'q light (see fig. 3), pure losses by respiration 

 only come iiilo question for a shorter portion of the night. No 

 completely reliable calculation of the extenl of the daily produclion 

 of carbo-hydrates can be arrived at in regard lo the seaweed ve- 

 getation from the above figures. For Ihe CO2 concenlralion actually 

 alTecting the leaf is very dilficull to estimate, and so also is the 

 temperalure of the leaf. 



An equilibrium between respiration and assimilation is reached 



* Several earlier investigators have proved that the shade-plants have lower in- 

 tensities of respiration than the sun-plaiits (see e. g. Lamartiére 1892, Ad. Meyer 

 1892. Hesselman 1904, p. 4n0). 



* These values can only be regarded as approximate. A similar series for 

 Deoraark has heen given hy P.oysens.Iensen (1918, p. 284). As I have not fixed 

 my uuit of light in any of the mbuhI scales, my light-values are not exactly com- 

 parable with those of any otlier investigator. However, the differences in the in- 

 tensity of the maximum light of heiiven hecome great only if two places lie on 

 very different degrees of latitnde or at differeut heights ahove sea-level. 



