384 



The light- umi (ia)-l-<jrointii-resiiiin.fe of coit'opfil/'.^ 

 of Avena sativo. 



By means of the experimeiiis of V'ogt, Sikkp and KoNiNtiSBEKGEu 

 a light-growtli-iesponsp lias been ascerlained. On applioalion of 90 

 MK on 3 sides Koningsbekokr finds a niiniinnni of about 55°/„ 35 — 40 

 minutes after the begimiiiig of the exposure — uext a maximum 

 after about 65 — 70 minutes (about 80 "/o "' '''^ '''-'e of growth in 

 dark) — while after 90 minutes a second minimum occurs amounting 

 to about 65 — 70° ,, of the rate of growtii in dark. Tiie latter iiow- 

 ever continues oscillating irregularly for houi-s together. In the figure 

 the curve of the light-growth-response is taken from an indivi<lual 

 of table 9 from Koningsberger's dissertation. 



Wliat reactioii oceurx, if ive darken after the rate of gronHli has 

 been in the main adapted to light for some hours? 



With Helianthns and Phyconiyces darkening appeared to cause 

 less intense changes of growth, than "Light". If this shoidd be the 

 case with the coleoptiles of Arena sativa, there would be danger 

 of this reaction finding no expression at all or but indistinctly, on 

 account of the irregular growth of Ji;«m, in consequence of occurring 

 nutations. 



We have therefore tried to eliminate or restrict these impeding 

 movements. Not oidy were a gieal number of Oat-races observed 

 in this respect, but also conditions of more or less moist and liot 

 cultivation were tried. In this way we have succeeded in finding 

 an Oat-race called "Zwarte President" which when cultivated in a 

 very dry soil but verj' rarely nutates inconveniently. As long as the 

 coleoptiles secrete little or no drops of moisture, the growth was 

 extraordinarily constant and frequently remained within the limits 

 fixed b}' US: no more than 10 7o variation of growth. The tempe- 

 rature at which the plants grew was about 22° C. In oider to give 

 a good idea of the results, obtained for this object, we decided to 

 give the whole of its individual responses of growth in this commu- 

 nication. Our preceding illumination was 4sided with 64 MK.. 

 which intensity deviates but little from that used by the above- 

 mentioned investigators. The rate of growth has been given in microns 

 per minute. ') 



N*. 1. Exposed beforehand for 4i hours at 21°,9 6'. to 64 jl/ZiT: 



I) The small tigures denote the time of observalion, by which the beginning 

 of darkening is again put at the full hour (60). 



