N 
1909] BORDNER—INFLUENCE OF TRACTION ON STEMS 273 
increase of both these mechanical tissues. The experimental evidence 
for Rubus occidentalis was too limited to be conclusive. The stems 
were already too old and mature when the experiment was started. 
The writer is convinced, however, by this experiment with Rubus 
occidentalis, that the tension used by WIEDERSHEIM (29) on pendant 
woody branches was not sufficient to send a stimulus past the stimulus 
threshold. 
UNIVERSITY OF MICHIGAN 
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ia) ul 
(aaa) 
am 
9 
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