266 



20' 

 19- 



I8' 



PLANT GROWTH SUBSTANCES 



CONC. ADENOSINE IN MG/L 

 T 1 1 1 1 r — I 1 



—I 



20 



Figure i. Effect of concentration of adenosine on the growth of tobacco 

 callus in vitro with and without addition of 0.25 mg./l. NAA. Exp. #14 

 started 12/24/43. Harvested 3/16/44. Data of 32 cultures for each treatment. 



later experiments increases were obtained in the number of callus tissues 

 forming buds as illustrated in Table 2. 



The addition of adenine similarly was found to stimulate the formation 

 of buds, and adenine is, in fact, more active than corresponding concen- 

 trations of adenosine (Table 3, compare also Fig. 7). 



The above results show that the inhibiting effect of auxin on bud 

 formation is reversibly counteracted and that the growth rate of callus 

 in the presence of added lAA is increased by the addition of adenine or 

 adenosine and phosphate. The results suggest, therefore, that auxin may 

 exert its eflect on growth through an action In one or more phosphoryla- 

 tion systems. 



Experiments tvith tobacco stem segment cultures. — The effects obtained 

 with treatments of lAA, adenine, and its derivatives on callus cultures 

 have been confirmed and the results considerably extended by experi- 

 ments with excised stem segments of tobacco. 



Young stems of variety Wis. #38 were surface sterilized, sectioned, 

 and cultured on White's nutrient medium as described by Skoog and 

 Tsui (11). This material was found to give clear-cut and reproducible 



