126 



GROWTH HORMONES IN PLANTS 



worked out the proportionality existing between its concentration 

 and the number of roots formed in pea seedlings (Fig. 39). 

 The details of the method may be obtained from Fig. 40. Thi- 

 mann and Went (1934) found that the active substance was 

 present in large quantities in the crude auxin extracts obtained 

 from Rhizopus and also from urine. Then it was found that the 





u + 



Jl20 KMn04 



4 hrs. 4 hrs. 



V 



Many per bottle 



C D 



Y 



s 



c 



n 



u + 



5 cc. 



1 cc. 

 Solution „ 

 to be tested 2 per cent sugar 



,j5 hrs. 



-Ji>ft 



6 days 



Five per bottle 

 G 



5 cc. 

 H2O 

 7 days j 



H 



I 



f) 



A+ 



Fig. 40. — A method of testing for the presence of substances stimulating the 

 production of roots. The number of roots formed indicates the approximate 

 effectiveness of the solution. The test is made in a darkroom at 25°C. and at a 

 relative humidity of 60 to 70 per cent. A, etiolated pea seedling 7 days old, 

 cut above first scale leaf and again just below the tip, gives test plant B. Basal 

 end of shoot marked +. After standing in water 4 hours, C, and in potassium 

 permanganate 4 hours, D, the shoot, E, is split longitudinally at the apical end 

 with a sharp razor blade, and the base rinsed with water. It is immersed 

 15 hours in the solution to be tested, then rinsed with water and placed in sugar 

 solution where it is allowed to stand for 6 days, G. Next it is removed from the 

 sugar solution, rinsed with water and placed in water for 7 days, H. Two weeks 

 after stage A, the test plant I is examined for the number of roots present. 

 (After Went, 19346.) 



pure auxins prepared by Kogl and coworkers were effective in 

 root formation (Thimann and Went, 1934) as well as in growth 

 promotion. Thimann and Koepfli (1935) showed that 3-indole 

 acetic acid stimulates root production; hence substances causing 

 cell elongation are also effective in root formation. The role 

 of pollen and urine extracts in root formation has been studied 

 further by Muller (1935) and by Laibach and Fischnich (19356). 



