Extraction and Measurement Techniques 23 



is not available, simply placing the plants in front of photosensitive 

 projection paper and exposing to a 40-watt bulb approximately 10 

 feet away for 3 seconds will be effective. The apparatus shown in the 

 figure, however, is desirable for best photographic detail. 



6. A protractor, as in figure 10, with which to read the curvatures 

 as recorded on the shadowgraph. 



Fig. 10. Simple protractor made of clear plastic for measuring curvature in Avena 



test. 



Pure agar is used at a concentration in water of 1.5 per cent. It is 

 very important that the percentage be held constant within any test. 

 Lower concentrations of agar produce more curvature per unit of 

 auxin, thus the lower the concentration of agar used the greater the 

 sensitivity to small quantities of auxin. However, the linear relation- 

 ship between the quantity of auxin and curvature obtained is best at 

 approximately 2 per cent agar. Consequently, in order to obtain 

 highest sensitivity and yet to approximate linearity in response, a 

 1.5 per cent agar is accepted as being best. To prepare the agar 

 the weighed, dry material is added to water and carefully heated in 

 a water bath until a uniform translucence is obtained. 



PROCEDURE FOR THE AVENA TEST 



Planting 



Place husked seeds of Victory oats in water in a suction flask and evacuate three 

 times on the water tap. If the husks are left on, poor or no germination will result. 

 Let them soak for about two hours, then discard the soak water, as it contains auxin 

 released by the germinating seeds. On glass plates covered with wet paper toweling, 

 place the seeds groove-side down, and embryo end projecting slightly over the edge 

 of the plate. Put glass in germinating dish in darkroom (25° C), add water to 



