396 VEGETABLE PHYSIOLOGY 
during natural life the plant is receiving coincidently several 
kinds of stimulation, the effect of some being not infre- 
quently antagonistic to that of others. It is not easy to 
discriminate between these, nor to say how the influence of 
each helps to determine the resultant response. This is the 
more difficult as not only the stimuli themselves but their 
relative potencies differ continually. 
