59 



CHAPTEE VIII 



PLANT RESPONSE ON THE INFLUENCE OF TEMPEEATURE 



Effect of very low temperature Influence of high temperature Determi- 

 nation of death-point Increased response as after-effect of temperature 

 variation Death of plant and abolition of response by the action of 

 steam. 



FOR every plant there is a range of temperature most 

 favourable to its vital activity. Above this optimum, the 

 vital activity diminishes, till a maximum is reached, 

 when it ceases altogether, and if this point be maintained 

 for a long time the plant is apt to be killed. Similarly, 

 the vital activity is diminished if the temperature be 

 lowered below the optimum, and again, at a minimum 

 point it ceases, while below this minimum the plant may 

 be killed. We may regard these maximum and minimum 

 temperatures as the death- points. Some plants can 

 resist these extremes better than others. Length of 

 exposure, it should however be remembered, is also a 

 determining factor in the question as to whether or not 

 the plant shall survive unfavourable conditions of tem- 

 perature Thus we have hardy plants, and plants 

 that are affected by excessive variations of temperature. 

 Within the characteristic power of the species, there 

 may be, again, a certain amount of individual difference. 

 These facts being known, I was anxious to deter- 



