( 382 ) 



results as- well as by its violent coiiflict with the results of Fitting') 

 offers ample induceineut to subject this alleged localisation of the 

 transmission of phototropic stimuli to a new inquiry. 



So far as concerns experiments in the atmosphere of a room of 

 usual humidity and temperature, my experiments were carried out 

 in just the same conditions as those of Boysen Jensen; they took 

 place in the phototropic room of the laboratory building, at a 

 temperature of 17° C. and a humidity of 70 7o- The illumination 

 was always with the very suitable amount of energy of 400 candle- 

 meter seconds. 



The phototropic curvature effect which was produced by unilateral 

 illumination of the apex, transmits itself in the course of a certain 

 time to the base, a phenomenon that since Darwin is interpreted as 

 the transmission of the phototropic stimulus. 



Now if Boysen Jensen makes a transverse incision on the illuminated 

 side, which I will always speak of as the front or anterior side of 

 the coleoptile, then he sees that a basal curvature nevertheless, 

 arises in unilateral illumination of the apex. If on the other hand, 

 an incision is made on the posterior side he observes that ijj the 

 atmosphere of the room, onlj^ the apex curves phototropically, while 

 the base remains erect; in a space saturated with water vapour the 

 base indeed curves phototropically in the latter case, but the curvature 

 remains absent, when a mica plate is introduced into the incision. These 

 results cause Boysen Jensen to conclude that the stimulus is only 

 transmitted along the posterior side. Even in my very first experi- 

 ments I found that the influence of the incision is much greater than 

 might be concluded from Boysen Jensen's paper. When a unilateral 

 incision is made I perceived a really considerable curvature directed 

 to the side of the wound ; this curvature must probably be in part 

 put down to some traumatic stimulus, seeing that a curvature also 

 takes place in air saturated with water vapour; since in that case, 

 however the curvature occurs in much less degree, this is an 

 indication that in the ordinary room air the curvature is in the first 

 place due to the great amount of evaporation from the wound. This 

 view is still further confirmed by the following experiment. If we 

 make a unilateral incision and leave the coleoptile thus operated 

 upon for about half a day in a space saturated Avith water-vapour, 

 it will gradually recover from the cur\ature which had arisen ; 

 various coleoptiles then resume their normal erect position; not that 

 the wound itself closes through the apposition of the parts separated 



-) H. Fitting. Die Leitung tropislischer Reize in parallelolropen Pflanzenteilen. 

 (Jhrb. f. wiss. Bot. Bd. 44. 1907). 



