383 



At 64 MK the first reaction already appears after about 3| min., 

 the minimum amounting to 39 "/o. after 20 — 25 min., vvliile after 

 that the rate of growth gradually reverts to its initial value. 



Finally at 512 MK the reaction-period is 3^ minutes, the minimum, 

 now 21 "!„, appears after about half an hour ami conliiiues for a 

 long time. Even some hours after the beginning' of Mie exposure the 

 rate of growth remains considerably below the rale in dark. Compare 

 the figures subjoined. 



What reaction tahex place, nihen ire darken after these hypoco- 

 tyledovs have heen mainly adapted to a constant illumination for 

 5 — 7 hours? 



The results of these experiments, made at about 20° C. have been 

 briefly summarized in the subjoined table. 



TABLE III. 



After about an hour and a half the growth had become settled 

 again. As to the rate, putting together all data of 1, 64 and 512 MK 

 and comparing the rate of growth in light to the rate 1 — 2 hours 

 after darkening, we find of the 14 results: a retardation of growth 

 in 7, an acceleration in 6 and an unaltered rate in one, while an 

 average acceleration of growth of 5 ± 21 " „ may be computed. 

 Therefore the chances for the existence of a lasting acceleration of 

 growth may be called slight. 



On comparing the light- and dark-responses to each other (see 

 figure!), we are again struck by the reverse process, though there 

 is no perfect symmetry. In both cases the reaction is more marked 

 for higher intensities (lower minima, resp. higher maxima). 



Upon the whole the dark-response is not so strong as the light, 

 response. The reaction-period is longer, the change in growth less 

 intense, the external equilibrium of growth sooner restored. 



