THERMAL ADAPTATION 



1229 



philic" behavior. One of them grew fastest at 39° C; fig. 31. 8A shows its 

 growth rate as a function of temperature, compared to that of an ordinary 

 strain of CJdorella pyrenoidosa. The rate of growth of the two strains ap- 

 pears the same below 25° C, but the thermophihc strain grows much faster 

 at the higher temperatures; a much higher light intensity is needed to reach 

 growth "saturation" in this case. PreHminary manometric studies of the 

 thermophilic strain at 39° C. indicated a rate of glucose respiration equiv- 

 alent to 18 volumes of oxygen, and a rate of photosynthesis equivalent to 

 186 volumes of oxygen per volume of cells per hour (Sorokin 1954) — by 

 far the highest rate ever observed with any organism ! 



30 

 TEMPERATURE 



Fig. 3 1.8 A. Growth rates of an ordinary and a thermophilic strain of Chlorella 

 (Sorolcin and Myers 1953): (A) Chlorella pyrenoidosa (Emerson's strain) at 

 1600 foot-candles; (X) Tx 71105 at 1600 foot-candles; (O) Tx 71105 at 500 

 foot-candles; (0) Tx 71105 at 2800 foot-candles. 



We have spoken so far of the adaptation of whole species (or strains) 

 to heat or cold. As in the case of heliophilic and umbrophilic plants, this 

 "phylogenetic" thermal adaptation is paralleled, although on a reduced 

 scale, by the adaptation of individual organisms. Harder (1924) studied, 

 as an example, the behavior of the aquatic plants Elodea canadensis, 

 Fontinalis antipyretica, Hypnum, CJiara and Chladophora, grown at 4.6° and 



Table 31.11 

 Photosynthesis of Fontinalis Plants Grown at 4.6° and 20° C. (after Harder 1924) 



