GROWTH SUBSTANCES FOR OTHER PHENOMENA 125 



\'nn Her Lek, 1925. The presence of a developing bud 

 or young leaf promotes root formation in a woody 

 cutting. 



HV«(. 1929. A substance stimulating root production 

 is contributed to a stem by a grafted leaf, c, or agar con- 

 taining boiled diastase solution, h; the control stem, a, 

 remains without roots. 



Went, 1934b. Thimrnin and Koepfli, 1935. A 

 quantitative test for substances stimulating 

 root production may be made by immersing 

 the apex of a split stem in solution for 15 hours, 

 ."ifter two weeks' growth in water, the number 

 of roots gives a measure of the concentration of 

 the substance. (See Fig. 40 for further details.) 

 With this method, it was established that 

 rhizopin, auxins, and "rhizocaline" are 

 identical. 



Lfnbacli,MuUcr,nnd Sthdfir, 

 1934. Lnilmrh. 1935. Applica- 

 tion of 3-indole acetic acid 

 paste to a Coleus stem cau.ses 

 roots to be produced in great 

 numbers. 



Zimmerman and Wilcoxon, 1935. 

 Injection of indole acetic acid, naph- 

 thalene acetic acid, indole butyric 

 acid, etc., into plant stems stimulates 

 root production. 



Hitchrnck and Zimmerman, 1935. Addition 

 of 3-indole acetic acid or any one of several 

 other synthetic growth substances to the 

 soil stimulates root production on aerial 

 parts of Lycopcrsicon and Nicotiana. 



Zimmerman, Croeker, and 

 Httchcock. 1933. Treatment of 

 Tageles plants with 1.0 per cent 

 carbon monoxide mixed with 

 air for 2 to 10 days stimulated 

 the production of adventitious 

 roots on the stem. 



Zimmerman and Hitelieoek, 

 1933. Tageles: a, roots were pro- 

 duced six days after a 72-hour 

 treatment with 0.25 per cent 

 acetylene; b, a second treat- 

 ment with gas caused a change 

 in the direction of growth and 

 the production of root hairs. 



Fig. 39. — Rooting phenomena. 



