3fi4 



amount of Uglit-energy used as stiinulus. (Thus at 50 CM. S. tlie 

 reaction-time is 30 minutes, at 1 C. M, S. it is nearl}^ 2 hours.) 



x^lIso the maximum curvature which is reached, is a function of 

 the quantity of light-energy used as stimulus. 



The degree of curvature, which is reached after a certain time, 

 gives therefore (within these limits) a measure, by which conclusions 

 as to the magnitude of the stimulus may be drawn. 



These experiments have been continued further with greater 

 amounts of light and have yielded the results that might have been 

 expected. The reaction, which follows on stimulation with a definite 

 amount of light-energy, is constant for that quantity of energy, only 

 when the stimulus is applied for a comparatively short time. If the 

 quantity of energy is applied for a longer time, then so-called tone- 

 phenomena occur, which I intend shortly to discuss in greater detail. 



If the stimulus is more than 100 C. M. S. the degree of curvature 

 remains about the same. If however it is made considerably more, 

 as for example 1200 C. M. S. at 23° C, then the resulting curva- 

 ture is notably smaller ; this continues up to 6000 C. M. S. when 

 a new phenomenon api)ears, the negative curvature, which reaches 

 a maximum at about 18000 M. C. S. From the paper of van der 

 WoLK^) and the recent one of Wilschke^j it has been shown that 

 with these quantities of light positive curvatures from the base were 

 to be expected and since it further seemed desirable to exclude such 

 an intluence, light was prevented from reaching the base. To this 

 end there was placed round each seedling a black copper tube, which 



entirely due to the longer presentation-time with weak centrifugal forces. 

 For this case Maillefer (Bull. Soc. Vaud. Vol. 48 1912) has mathematically 

 deduced the formula i {t — k) = constant (the reaction-time equals the presentation- 

 time + a constant value.) This agrees with Bach's table 34, not with Mrs. Rut- 

 ten — Pekelharing's table 27. 



The lengthening of the reaction-time on stimulation during the whole reaction- 

 time is more complicated, because in that case neither the strength of the stimu- 

 lus (iXO> nor the duration (t) is constant. For this case Tröndle (Jahrb. f. Wiss. 

 Bd. 48 1910) has put forward the empirical formula i {i — k) = constant. 



This formula is not supported by the tables which Tröndle adduces as proof. 

 Nor does Bach's table 33 according to Tröndle give true values, whilst Bach's 

 table 32 gives constant reaction-times for which t = k. 



In Bach's tables 34 and Mrs Rutten— Pekelharing's table 27, as has 

 already been pointed out, stimulation was not continued during the whole 

 reaction-time. 



1) Publications sur la Pbysiologie végétale, Nimègue 1912. 



2) Sitzungsberichte K. Akad. Wien, Bd. 122, 1913. 



