( 335 ) 



localisaüon hypothesis is correct, if l\y the cut on the poslerior side, 

 provided with a mica pUite, die phototropic connection between the 

 l')ase and the apex is indeed broken, then it must still be a matter 

 of inditference to the base, wliether the coleoptile is illuminated or 

 not. Now, however, since we see that on illuminating the apex, the 

 base does not curve towards the side of the wound, the suspicion 

 arises that there is still, along the front side of the coleo[)tilc, a 

 transmissi(jn of the phototropic effect. This suspicion vvcis confirmed 

 when in addition to that on the posterior side, an anterior cut was 

 made and was provided with a mica plate, so that the alleged 

 transmission in front would be inhibited. I have carried out the 

 experiment in such a way that I made first a cut on tiie anterior 

 side, after which I let the plant recover from the operation as 

 described above, for about three-quarters of a day in a space 

 saturated with water-vapour, so that it again became erect. Then 

 on the posterior side a cut was made and provided with a mica- 

 plate ; immediately afterwards the apex was illuminated, while for the 

 rest I allowed the plant to remain in the ordinai-y air of the room. 

 This is therefore really the fundamental experiment of Boysen 

 Jensen, only with the difference, that by taking special precautions, 

 transmission on the front side is also prevented. The result of this 

 experiment was again completely convincing; the base now curved 

 indeed towards the side of the wound in spite of the illumination 

 at the apex. The cut on the anterior side indeed exerts an influence, 

 but the fresh cut on the posterior side preponderates and over-rides 

 also the transmission of stimulus which possibly might have taken 

 place from both incisions. This result furnishes ])roof that by the 

 cut on the front side "something" is really held back which before 

 prevented the base from curving towards the side of the wound. 

 What can this "something" be other than a phototropic curvature 

 effect? Therefore here also on the anterior side transmission of 

 stimulus takes place. 



The following experiment furnishes direct proof that the trans- 

 mission of stimulus can take place anywhere. In contrast with the 

 foregoing experiment a cut with the arrangement of mica-plate was 

 made both in front and behind, whilst the seedlings during the 

 whole experiment remain in the ordinary air of the room, this 

 again being an experiment, similar to Boysen Jensen's initial experi- 

 ment, with the difference that the unilateral influence of the cut on 

 the posterior side is inhibited by a cut on the anterior side. Control 

 experiments indeed show that in such an experiment, without 

 further illumination, the base remains erect. Suppose we now 



