supply of light. I have investigated tiic influence of omnilateral 

 fore-illninination by allowing the plants to rotate for various periods 

 of time at 5 diifcrent intensities, of 5.5, 12.1, 25, 100 and 450 

 candle metre power. The i-esults of the first four series ai-e summa- 

 rized in tables. Without going into points of agreement and difïerence, 

 which would require detailed discussion, I here only wish to remark, 

 that Table I is comparable with the investigation of Pringsheim 

 (second paper IV) and that my table !II shows agreement with 

 Clark's figure 2. 



It is especially by a consideration of table I, where the preliminary 

 illumijialion is weakest, namely 5.5 candle metre power, that we 

 can most readily obtain some idea of the influence of omnilateral 

 fore-illumination. A survey of the first six vertical columns of this 

 table, in which the unilateral after-illumination was 22 — 1000 CM. S., 

 reveals that a fore-illumination of 100 seconds already requires an 

 after-illumination of 60 C. M. S. to bring about a curvature, whereas 

 after 10 seconds 22 C. M. S. were able to do this. After still longer 

 preliminary illumination not much more energy need be supplied 

 and 120 C. M. S. always gives a definite positive curvature. We 

 may therefore conclude that the sensitiveness has been diminished 

 by the fore-illumination. 



A second phenomenon is observed when the amonnt of the energy 

 of the after-illumination is increased (the last three columns of 

 table I). As I have previously^) shown these large amounts of energy 

 (more than 4000 C M. S.) bring about negative curvatures. Even 

 after brief fore-illumination these negative curvatures occur after 

 large amounts of energy, but now the phenomenon is observed, that 

 after preliminary exposures of 5 minutes or longer, these negative 

 curvatures become feebler, and already after 20 minutes they are 

 no longer obtainable. Then positive curvatures occur, which are 

 extremely feeble at 27000 C. M. S. and become more clearly visible 

 at 13500 and 4500 C. M. S. After 1 hour's fore-illumination the 

 positive curvature is even very marked at 4500 C. M. S. 



This second phenomenon, which, as will be explained more fully 

 at the end of this paper, I wish to consider as the typical "adjustment 

 phenomenon'' must therefore be formulated as the fact, that after a 

 certain duration of the preliminary exposure, it is no longer possible 

 to obtain negative curvatures at a certain intensitj' of unilateral 

 after-illumination. 



If w^e compare with this the other tables we find that also at 



^) Proc. Kon. Akad. v. Wetensch. Amsterdam Sept. 1913. 



