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becomes straight and the curvature in the base has become fixed. 
Perhaps we possess therefore in this method of observation with 
an intermittent clinostat a more accurate means of determining the 
sensitiveness of the plant. 
If we once more trace how far the above investigations influence 
our conception of the process of stimulation, it is clear that the 
comparability with physico-chemical processes becomes more and more 
marked. The existence of a threshold of stimulation can no longer 
be maintained, for not only is each quantity of energy perceived but 
it is clear now that a reaction will always take place. The time 
which intervenes between the application of the stimulus and the 
