8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 97 



at least, the form of the curve may vary greatly according to the 

 technique used. No evidence of a similar situation in the straight 

 growth response has been obtained as yet. 



DISCUSSION 



In addition to the theoretical preferability of Utilizing straight 

 growth rather than curvature, the present method offers several tech- 

 nical advantages. The usual glass holders, which are time-consuming 

 to make, difficult to clean and easily broken, are eliminated. The solid 



^ ° o o 



0.05 0.10 0.15 0.20 



CONCENTRATION INDOLE -3-ACETlC ACID (MG/LITER) 



Fig. I. — Relation between concentration of applied growth substance 

 and straight growth. 



root medium provides firm anchorage for the seedlings which facili- 

 tates the operations of decapitation, removal of the leaf, and applica- 

 tion of the block. The use of test tubes greatly expedites the removal 

 and rearrangement of the plants in the racks in preparing uniform 

 sets. The large test blocks are more easily applied and make better 

 contact when applied terminally. No handling of the seedlings is 

 necessary between the time of initial planting and of testing. 



These practical advantages, as well as some others, apply also to the 

 use of agar in test tubes for the growth of seedlings to be used in the 

 curvature test. The seeds may be planted very close to the top of the 

 tubes so that practically none of the coleoptile is obscured in photo- 

 graphing. The tubes allow the plant to be revolved about its long axis 



