RESPIRATION 



297 



but this is not always the case, for reasons which will be made clear 

 below. 



Conditions Influencing Respiration. — Temperature is one of 

 the chief controlling factors in respiration. Plants in the dormant 

 state give off only small quantities of carbon dioxide and in such 

 circumstances can stand much lower temperatures than when 

 active. Seeds have been placed in liquified gases at a tempera- 

 ture of — 250° C. and have survived, showing that respiration must 

 have gone on even slowly at that low temperature. Respiration 

 increases up to about 40° as shown by Fig. 18, prepared from tables 

 mgs. 



10 20 30 40 C. 



Fig. 18. — Illustrating increase in respiration with temperature. Milligrams 

 of carbon dioxide given off by two grams of cherry laurel leaves per hour at 

 the temperatures cited. (From data of Matthaei.) 



by Matthaei (1904). After this temperature has been reached, 

 respiration diminishes slowly until the death of the organism 

 takes place, when it may continue for some time at a fairly rapid 

 rate. The cause for the decrease after 40° is probably some injury 

 to the protoplasm or to the respiratory enzymes. Gerhart (1930) 

 found with strawberries that the temperature coefficient of respira- 

 tion was 2.5 between 5 and 25° C. These figures agree moderately 

 well with those of other workers on various plant materials. 



Fluctuations in temperature also cause increases in respiration. 

 If a plant is kept for some time at a high temperature and then 



