l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



The phototropic sensitivity curve rises sharply from 4100 A to a 

 maximum at 4400 A. It then drops off to a minimum at about 4575 A 

 and again rises to a secondary maximum in the region 4700 to 4800 A. 

 The fall is very rapid from this |3oint to 5000 A, from where it tapers 

 off very gradually to the threshold on the long-wave-length side at 

 about 5461 A. 



Phototropism, because of its photochemical nature, its relation to 

 auxins and the fact that it is a specific light-growth reaction, places 

 in the hands of the experimenter an important tool for investigating 

 the fundamental relationship of plant growth processes to light. 



LITERATURE CITED 



Bachmann, Fr., and Bergann, Fr. 



1930. t)ber die Werkigkeit von Strahlen verschiedener Wellenlange fiir die 



phototropische Reizung von Avena safiva. Planta, Arch. wiss. Bot., 



vol. 10, pp. 744-755- 

 Bergann, Friedrich. 



1930. Untersuchungen iiber Lichtwachstuni, Lichtkriimmug und Lichtabfall 



bei Avena sativa mit Hilfe monochroniatischen Lichtes. Planta, 

 Arch. wiss. Bot., vol. 10, pp. 666-743. 

 Blaauw, a. H. 



1909. Die Perzeption des Lichtes. Rec. Trav. bot. neerl., vol. 5, pp. 209-372. 



1914. Licht und Wachstum. I. Zeitschr. Bot., vol. 6, pp. 641-703. 



1915. Licht und Wachstum. II. Zeitschr. Bot., vol. 7, pp. 465-532. 



1919. Licht und Wachstum. III. Die Erklarung des Phototropismus. Med. 

 Landbouwhoogeschool, Wageningen, vol. 15, pp. 89-204. 

 Castle, E. S. 



1931. The phototropic sensitivity of Phycomyces as related to wave length. 



Journ. Gen. Physiol., vol. 14, pp. 701-711. 

 Flint, Lewis H. 



1934. Light in relation to dormancy and germination in lettuce seed. Sci- 

 ence, vol. 80, pp. 38-40. 

 HuRD, Annie May. 



191 9. Some orienting effects of monochromatic lights of equal intensities on 

 fucus spores and rhizoids. Proc. Nat. Acad. Sci., vol. 5, pp. 201-206. 

 Johnston, Earl S. 



1926. A plant photometer. Plant Physiol., vol. i, pp. 89-90. 

 1931. A quantitative determination of phototropic response to wave length. 

 (Paper presented at meeting of the Amer. Soc. Plant Physiol., 

 New Orleans, La., Dec. 29.) 

 Johnston, Earl S., Brackett, F. S., and Hoover, W. H. 



1931. Relation of phototropism to the wave length of light. Plant Physiol., 

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 KoGL, Fritz. 



1933. On plant growth hormones {auxin A and auxin B). Rep. British 

 Assoc. Adv. Sci., vol. 1933, pp. 600-609. 



