ON CONTACT IRRITABILITY 
BY 
ALFRED J. EWART. D. Sc., Ph. D. 
Deputy Professor of Botany in Mason’s College, Birmingham. 
With pl. XVIII and XIX, 
The following work was carried out at the suggestion of 
Dr. Trevs during a stay at the Buitenzorg gardens, Java, and 
was primarily intended to be a research into the physiology of 
hook climbers; but as the work during the investigation branched 
out in several allied directions, it has seemed best to incorpo- 
rate the whole under the general heading ,Contact Irritability”. 
It was Trevs’s paper on hook climbers?) that first called the 
attention of the botanical world to the fact, that the hooks 
of certain climbers became, when fixed to a support, thicker 
and stronger. Trevs was occupied mainly with the morpholo- 
gical side of the question, contenting himself with indicating 
broadly the lines, which the necessary subsequent physiological 
inquiry must follow. 
The points to be determined were many, viz. the irritability 
of the different parts and surfaces of the hook, the minimal 
and maximal stimuli, the relative effects of pressure and con- 
tact, the influence exerted by the nature of the surface in 
Contact, the rapidity of the response to stimulation, the trans- 
mission of the stimulus, the strength of the mature attached 
hook and the strain which it is capable of bearing, and the 
relative amounts of growth caused by stimuli varying in nature 
es 
1) Ann. du Jard. Bot. de Buitenzorg. II. 1882. 
