169 



set 1 : 900 mg.-secs. i.e. the seedlings remained for 

 1 5 minutes in a horizontal position ; 

 set 2: 40 M.C.-secs. i.e. the seedlings were exposed 

 for 8 seconds to the action of a 

 lamp of 5 candie power at a 

 distance of 1 mètre; 

 set 3: 600 mg.-secs. i.e. the seedlings remained for 

 10 minutes in a horizontal position ; 

 set 4: 400 M.C.-secs. i.e. an exposure of 80 seconds 

 to the lamp of 5 candie power 

 at a distance of 1 m. 

 The duration of the stimulation was determined accura- 

 tely by means of a stop-watch. 



Àfter this I traced the extent of the maximal curvatures 

 which correspond to thèse quantities of energy, and the 

 length of the periods which elapse between the beginning 

 of stimulation and the time at which the maximal cur- 

 vature was reached, i.e. the reaction times. For Àrisz ^)' 

 experiments hâve shown that to each quantity of energy 

 there belongs a maximal curvature of definite extent and 

 a definite curvature time. The extent of the curvature 

 was expressed by the perpendicular déviation of the apex 

 from the vertical, measured over the centre of the coleop- 

 tile. This measurement was made by placing a strip of 

 paper marked in millimètres behind the coleoptile. A few 

 preparatory experiments showed after about what interval 

 of time the maximal curvature became visible. In order 

 to détermine this curvature-time accurately, the boxes 

 containing seedlings were taken out of the thermostat after 

 différent intervais and the curvatures were measured. I 

 tried to narrow the limits deflning the time at which 

 maximal curvature appeared; Thus I first measured the 



') W. H. Arisz. Untcrsuchungen ûber den Phototropismus. Recueil 

 des Trav. Botan. Néerland., 1915, Vol. XII. p. 44. 



