2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



cussion of the growth substance literature the reader should consult 

 Boysen Jensen's (1936a) English translation of "Die Wuchs- 

 stofftheorie." 



The studies recorded in this paper attempt to show whether the 

 function of light in phototropism and morphogenesis is primarily 

 concerned with the redistribution of plant growth substance (hor- 

 mone), or with its inactivation. 



MATERIALS AND METHODS 



The following plant materials were used in the experiments : 

 Seedlings of Avena sativa, varieties Victory and Markton ; seedlings 

 of Zea mays, a sugar endosperm type known as Connecticut No. 2 ; 

 and terminal shoots of young Nicotiana tabacimi. The oat seeds were 

 supplied through the kindness of Mr. T, Ray Stanton and the tobacco 

 plants by Dr. J. E. McMurtrey, Jr., United States Department of 

 Agriculture, Washington, D. C. The seedlings were grown in a 

 darkroom operated at 80° F. and 90 percent humidity. Only photo- 

 tropically inactive orange-red light (Wratten Safelight Series O) 

 was used to facilitate making the various necessary manipulations. A 

 water-culture technique modified after the method of F. W. Went 

 (1928) was used for gro\ving the oats. Corn seedlings were grown 

 in sandy soil contained in clay pots. 



Apparatus for the water cultures is illustrated in plates i and 2. 

 The portable tray shown in plate 2 proved to be very convenient in 

 carrying out the various experiments. The essential parts of this 

 tray are a wooden frame, waterproofed with paraffin, phosphor-bronze 

 spring clamps, glass holders, and a Pyrex glass water cell designed to 

 accommodate the roots of 10 oat plants. Paraffined zinc water cells 

 were used in a few supplementary experiments. Distilled water was 

 used in all these cells. As may be seen in plate i, the glass holders 

 were made with care so as .to hold the oat seeds firmly and permit 

 an ample portion of the sprout to project through and above the 

 glass collar. The diameter of rod, and size and tension of the 

 spring clamps were standardized so as to permit exchangeability and 

 easy adjustment of position in the racks. Thus the technique becomes 

 practically free from objectionable features so that uniform test 

 plants may be obtained repeatedly. 



Seedlings of Avena were grown as follows : Seeds with the chafif 

 removed and selected for uniform size were soaked in distilled water 

 for 4 hours, and then placed each with the grooved side down 

 about one-half inch apart on moist filter paper in petri dishes. They 



