Extraction and Measurement Techniques 31 

 erate the physiological tip. Slitting the stems and soaking them in 

 water for an hour or more removes tor all practical purposes the auxin 

 supply naturally present in the stems. By this means a specimen highly 

 sensitive to added auxin is obtained. 



I'he environmental controls required lor the slit pea test aie 

 simpler than those lor the Avena test. Since the material is tested in 

 solution, there is no need for humidity control. Temperature sensi- 

 tivity is very much lower than in the Aveyia test. Small amounts (j1 

 diffuse white light do not alter the results. 



Fig. 14. Tools for the slit pea test. Left: Cutting block for convenience in slitting 

 stems, holds razor in slanted position and provides guide for uniform length of cut. 

 Right: Simple protractor for reading curvatures. (Adapted from van Overbeek and 

 Went, 1937.) 



The materials required are as follows: 



1. Alaska peas or other pure strain of pea seed. 



2. Porcelain trays or sterile wood flats for culturing seedlings. 

 Because of the great sensitivity of this test to metallic ions, the 

 plants should not contact any bare metal. Hard maple sawdust 

 (steam sterilized) or washed sand is frequently used as a med- 

 ium for the plant's culture. Vermiculite makes a very conve- 

 nient medium and can be discarded after use. 



3. A cutting block such as that illustrated in figure 14. This item 

 is not essential, and instead an ordinary razor blade may be 

 used, though with somewhat less convenience. 



4. A 360° protractor, easily fashioned from a piece of glass, as 

 shown in figure 14. 



PROCEDURE FOR THE SLIT PEA TEST 



Planting 



Into a porcelain-ware tray, place about one-half inch of dry vermiculite or 

 sand. Saturate with water. Scatter seeds of Alaska pea evenly over the vermiculite. 



