1244 



THE TEMPERATURE FACTOR 



CHAP. 31 



supply of carbon dioxide, and two subsidiary maxima at 20° and 10°; in weak light 

 (e. g., 1/25 of full sunlight) and relatively low carbon dioxide concentration (e. g., 

 0.03%), the 20° maximum became more prominent than the one at 30°. 



Subsequent studies of bean leaves by Yoshii (1928) and of barley leaves by Beljakov 

 (1930) — in Lundegardh's laboratory — also gave temperature curves with several 

 maxima. An example is shown in figure 31.15. Beljakov found that the relative promi- 

 nence of the two main maxima — in the region of 20° and 30° C. — was different for two 

 barley strains, and he considered this a sign of phylogenetic adaptation to dilTerent cli- 

 matic conditions. 



Stocker (1927) found two maxima in the temperature curves of northern lichens 

 (thus confirming the observation of Henrici with alpine lichens) and later (1935) also 



22 



21 



< 



18 



o 

 o 



d. 15 



E 



o 



< 



12 18 24 30 36 



TEMPERATURE, °C. 



42 



Fig. 31.15. Temperature curves of bean leaves showing 

 several maxima (after Yoshii 1925). 



in the temperature curves of tropical trees. Stalfelt (1939), however, found only one 

 optimum for northern lichens (c/. fig. 31.1). Ehrke (1929, 1931) found very irregular 

 temperatures curves, with several "waves," for marine algae (e. g., the brown Fucus 

 and the red Plocamium). Similar curves were obtained by him also for the respiration 

 of these algae — a process for which a smooth ascent to an optimum is generally accepted. 



We strongly doubt whether the multiple maxima of Henrici, Lunde- 

 gardh, Stocker and Ehrke are at all real, and not caused by experimental 

 errors. Theoretically, no sequence of reactions with different temperature 

 coefficients can give rise to curves of this type ; it is, however, undoubtedly' 



