NO. II PHOTOTROPIC SENSITIVITY — JOHNSTON 7 



symmetrical, with the exception of the wave-length region being 

 investigated. A double-walled glass cylinder with water between the 

 walls slowly rotated about the axis of the coleoptile. Two strips of 

 paper blackened on the inside and separated i cm from each other 

 were wrapped about the cylinder in order to shield all but a restricted 

 region at the tip of the coleoptile from the light. The cylinder was 

 encased in a light-proof box which contained two oppositely placed 

 side windows. Through one window, light was passed from the 

 monochromator, and through the other, light from the standard lamp. 

 The standard used was a 200-watt, 50-volt projection Mazda lamp 

 with the filaments in a plane. The standard lamp was enclosed in an 

 air-cooled brass housing with one small glass window opening toward 

 the plant. The light from the standard was passed through a number 

 6.0 Corning line filter, a heat-absorbing glass, and a water cell before 

 entering the rotating cylinder surrounding the plant. The number 

 6.0 Corning line filter transmitted wave lengths from about 4400 A 

 to 5800 A and from 7000 A to 12800 A of the light transmitted by the 

 water filter. The radiation intensity of the standard was 0.37 micro- 

 watts/cm- at a distance of 25 cm. This value, of course, varied with 

 different lamps and also with the same lamp as it aged. A photo- 

 graphic red lamp was used behind the small rear window of the plant 

 box for properly placing a coleoptile at the beginning of each expo- 

 sure. Previous experiments showed the coleoptile to be insensitive 

 for all practical purposes to this particular light. The monochromator 

 lamp was located outside the phototropic room, which was a small 

 room with no outside walls located in the west basement of the Smith- 

 sonian building. Very little daily temperature fluctuation occurred 

 in this room because of its ideal location. 



Coleoptiles of oats, Avena sativa Culberson, were used in all these 

 experiments. The seeds were germinated at approximately 25° C. 

 between glass plates covered with moist filter paper. The plates were 

 so placed in moisture chambers that the seedlings grew vertically. A 

 careful selection of the seedlings was made for straightness when 

 they had attained a length of 2 to 4 cm. One was then transferred to 

 a small Erlenmeyer flask fitted with a cork stopper. It was supported 

 by means of a little cotton in a small hole of the stopper. The flask 

 was filled with distilled water so that the roots were entirely im- 

 mersed. With the cross hairs in a small telescope as a guide, the 

 seedling was adjusted to a vertical position within the glass cylinder 

 located between the two lights. 



The general experimental procedure was to illuminate the coleoptile 

 on its two opposite sides, preferably the narrow edges, and after a 



