iQ2o] OVERHOLSER & TAYLOR— TEMPERATURES 277 



environmental 



cardinal temperatures. 



It would not necessarily follow that the best temperature for 

 the greatest vegetative growth of pears, for example, would like- 



most 



and this is 



generally recognized by growers. Furthermore, the most favorable 

 temperature for the growth of the fruit on the tree may not be 

 the optimum for continued ripening of the fruit after harvesting, 

 with best flavor and resulting texture. 



Inhibition at high temperatures. — The fact is well known 



that metabolism, enzyme action, and other processes or functions 

 of the plant are to a certain point rapidly increased with a rise 

 in temperature. Blackman (4), however, has shown that the 

 maximum activity, especially for respiration and photosynthesis, 

 has commonly been placed too high, since proper consideration of 

 the time factor has not always been given. Above a certain 

 point it has also been clearly shown that high temperatures weaken 

 and lessen, general metabolic activities. 



From work done by Balls (2) it is possible that the inhibition 

 of growth at high temperatures during a considerable period of 

 time may be the result of an accumulation in the cells of injurious 

 metabolic products. Balls thinks that some of these deleterious 

 products are produced at low temperatures, but under such con- 

 ditions they are decomposed about as rapidly as formed. At high 

 temperatures, however, production is more rapid than decomposi- 

 tion, and accumulation takes place which results in the injury or 

 inhibition of metabolism. 



Gore (5), using temperatures from 2 to 35. 6° C, found the 

 rate of respiration increased an average of 2.376 times for each 



io° 



with 



different kinds of fruits. An interesting statement by Gore is 

 that "with many fruits the activity has been found to decline 

 when held at high temperatures/' 



Experiment 1 



AM EL 



minor similar experiments 



