NO. II ASSAY METHOD FOR GROWTH SUBSTANCES WEINTRAUB 9 



SO that the plane of curvature can be placed parallel to that of the photo- 

 graphic paper. Deseeding may be very easily accomplished with a small 

 section lifter or with forceps. 



Some disadvantages of the method should be mentioned also. The 

 size of the plants used is a relatively critical factor in comparative 

 studies. It has been found that with the uniform conditions employed 

 the time at which the seedlings will be ready for use can be predicted, 

 at the time of planting, to within 2 or 3 hours. It is essential that this 

 be considered in planning the various operations. The individual vari- 

 ability of the seeds used is such that only about 75 percent of the plants 

 are ready at one time. In a limited series, therefore, there will be con- 

 siderable waste. In an extended series of tests, involving a few hun- 

 dred plants, if the larger plants are used first the smaller ones will 

 attain a suitable size by the time they are needed so that more than 

 90 percent of the planted seeds can be utilized. 



SUMMARY 



An assay method for growth-promoting substances, which utilizes 

 straight growth of the Avena coleoptile, is described. The method 

 appears to possess a number of theoretical and practical advantages 

 over the widely used curvature test. 



LITERATURE CITED 



Avery, G. S., Jr., Burkholder, P. R., and Creighton, H. B. 



1937. Avena coleoptile curvature in relation to different concentrations of 



certain synthetic substances. Amer. Journ. Bot., vol. 24, no. 4, 



pp. 226-232. 

 Boysen-Jensen, p. 



1936. Growth hormones in plants. English translation by G. S. Avery, Jr., 



and P. R. Burkholder. McGraw-Hill Book Co. 

 DuBuy, H. G. 



1938. A method for extracting growth substances from pigmented tissues. 



Journ. Agr. Res., vol. 56, no. 2, pp. 155-158. 

 Schneider, C. L., and Went, F. W. 



1938. A photokymograph for the analysis of the Avena test. Bot. Gaz., 



vol. 99, no. 3, pp. 470-496. 

 Thimann, K. v., and Bonner, J. 



1932. Studies on the growth hormone of plants. II. The entry of growth 



substance into the plant. Proc. Nat. Acad. Sci., vol. 18, pp. 692-701. 



1933. The mechanism of the action of the growth substance of plants. 



Proc. Roy. Soc, ser. B, vol. 113, pp. 126-149. 

 Thimann, K. V., and Schneider, C. L. 



1938. The role of salts, hydrogen-ion concentration, and agar in the re- 

 sponse of the Avena coleoptile to auxins. Amer. Journ. Bot., vol. 

 25, no. 4, pp. 270-280. 



