188 PHYTOHORMONES 



node and, after washing, their bases are immersed in 0.05 

 per cent permanganate for four hours. This treatment dis- 

 infects the cuttings and improves their keeping quahty; it 

 also, according to Curtis (1918), improves rooting. The 

 terminal bud is then removed, and the apex of the stem, 

 split longitudinally for 1-2 cm., is immersed for fifteen 

 hours in 1 cc. of the test solution or extract (see Figure 52). 



Fig. 53. Root formation on etiolated pea stems 

 8 days after the treatment of Figure 52. Group 5, 

 10 mg. ; group 7, 100 mg. indole-3-acetic acid per liter; 

 group 9, water. Note auxin curvatures of slit tops in 

 5 and 7. Ten plants per group. 



The test solution is applied at the apex because the sub- 

 stance is transported polarly from apex to base, as shown 

 above. Only with very high concentrations of active sub- 

 stances can roots be formed by application at the base (see 

 XI E). After the treatment, the split apex is rinsed. If the 

 test solution contained auxin, the split halves will show the 

 inward curvature described in III D. Finally the cuttings 



