388 



response, i.e. tlie oscillations of growth remained of the size also 

 occnrring in constant ciicnnistances (smaller than J()°/„). With a 

 reservation as to the existence of snch an exceedingly slight reac- 

 tion, we may observe, that the lack of a lightgrowth-response goes 

 together with the lack of a dark-growth-response. 



S Ü M M A R Y. 



J . With the organs observed the occurrence of a. liyht-groivth- 

 response iveni together with a dark-growth-response, in the main con- 

 trary to the former. 



2. The Jack of u light-groivth-response [Avena-root] goes together 

 with the lack of a (/ark-growfh-response. This going together seeins 

 to hold good also individually {Sinapis-i-oot 500 MK.). 



3. With Phycomyces, Avena, coleoptile and Helianthus-hypocotyledon 

 the dark-groivth-7-esponse is less intensive than the light-groiiith-response : 

 the loaves have smaller amplitude and are of shorter duration s-o 

 that externally a constant rate of groivth is sooner attained. 



It remains to be investigated into, whether the inward eqnilibrium 

 is likewise sooner restored than the externally observable light- 

 growth-response. Eqnilibi'inm in the inward processes indeed does 

 not coincide with the appearance of a constant rale of growth to 

 be judged by the observer (7). 



With regard to the word "dark-growlh-response", used for con- 

 venience, sake, it should be hoi'ue in mind, that dark as such does 

 not cause the response: dark itself is not a stimulus, hut the modip- 

 cation in energy-supply, either when suddenly occiCrring (light-grou^th- 

 response), or suddenly ceasing (dark-groioth-response), respect, increasing 

 or decreasing. 



It may be easily understood, that stoppage of energy-supply causes 

 a slighter and shorter reaction in an organ, i.e. it sooner settles 

 down than when energy is supplied. 



LITERATURE. 



1 and 2. Blaauw, A. H. Licht u. Wachstum I en II (Zeitschrift f. Bot. 1914, 

 6 und 1915, 7). 



3. Blaauw, A. H. Licht u. Wachstum III (Med. d. Landb. Hoogesch. 1918, 15). 



4. Koningsberger, V. J. Tropismus u. Wachstum (Dissertatie. Litrecht, 1922). 



5. SiERP, H. Ein Beilrag zur Kenntniss des Einflusses des Lichts auf das Wach- 

 stum der Koleoptile von Avena saliva (Zeitschr. f. Bot. 1918, 10). 



6. SiERP, H. Untersuchungen iiber die durch Licht und Dunkel hervorgerufen 

 Wachstumsreaklionen bei der Koleoptile von Avena saliva (Eb. 1921, 13). 



