( 328 ) 



temperatures and with greater degree of moisture than is usually the 

 case, but all this with favourable results to the experimental material. 

 A further great advantage as regards technique was due to the 

 quicker course of separate experiments, a point to which in this 

 paper further reference will be made. 



By means of a ventilator fresh air is introduced directly from 

 outside, so that the atmosphere in the phototropic room always 

 remains pure; at the same time the temperature can be maintained 

 more or less constant, for without ventilation the temperature would 

 be raised as a result of the burning of red lights. The lighting is 

 done electrically so that, brieily, this phototropic room is entirely 

 arranged in accordance with the requirements of modern investigation 

 on the physiology of stimulation. 



In this section I must at the outset call attention to an important 

 phenomenon that has not yet been observed by investigators of 

 stimulation-phenomena and that can give rise and doubtless has given 

 rise to faulty or at least to unreliable results. I refer here to the 

 great sensitiveness of the coleoptile of Avena to contact-stimulation, 

 an observation which may perhaps in the future be extended to 

 other seedlings. This sensitiveness to contact-stimulation was first 

 noticed when it w^as found that phototropic curvatures can be 

 inhibited by rut bing with the finger on the non-illuminated side. 

 Smce I was fully occupied with other experiments, a further investi- 

 gation of this newly-discovered phenomenon was postponed, and I 

 limited myself to a few very preliminary experiments, with the 

 intention of obtaining a rough idea of the nature and degree of this 

 sensitiveness to contact-stimulation. With some objects of widely 

 differing degrees of hardjiess the coleoptile was rubbed on one side, 

 in red light, while light stimulation was excluded. The following 

 table shows the results obtained. 



