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CHAPTER VIIL 

PLANT RESPONSE—ON THE INFLUENCE OF TEMPERATURE 
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 pomt 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- 
