682 



L. G. Nickell and W. R. Tulecke 



Table 4. The eff"ect of gibbcrellin and 2,4-D on the 

 growth of tobacco and sunflower crown-gall tissues in LP 

 medium. 



* Ratio of fresh weight at end of test over initial fresh 

 weight. 



are presented in Table 5. Avocado is killed by gibberellin alone or 

 in the presence of 2,4-D, and its effect is apparently independent of 

 the level of 2,4-D used. The growth of broad bean is increased by 

 gibberellin. This effect is found in the presence or absence of 2,4-D. 



DISCUSSION 



The growth response of intact plants to applied gibberellins is 

 characterized by high sensitivity and considerable variability from 

 one type of plant to another. Similar responses of plant tissue cul- 

 tures are also observed in the presence of gibberellins. No strict cor- 

 relation was found between the response to applied gibberellin and 

 the inciting agent of tissue growth, the age of the culture, the type of 

 medium, or the plant part from which cultures were obtained. Netien 

 (6, 7) and Henderson (3) foimd the gibberellins inhibitory to the 

 growth of plant tissue cultures of Scorzonera, Dauciis, Rubus, Helian- 

 thiis tuberosus, and H. annuus. Schroeder and Spector (10), on the 

 other hand, obtained a significant growth increase at 5 to 25 p. p.m. 

 gibberellin with fresh explants of the mesocarp of Citrus medica. 



The results from tlie pollen tissues of Taxus and Ginkgo are in 

 agreement with the work of Chandler (2), who found that the pollens 

 of some plants were stimulated in germination and tube elongation, 

 while other pollens were retarded. Growth of the Ginkgo pollen tis- 

 sue was increased by the addition of 10 p.p.m. gibberellin to the basal 

 medium; this was true for two strains of the tissue. Taxus pollen tis- 

 sue, on the other hand, was retarded. 



An interesting observation is the effect of gibberellin on die color 

 of all bean cultures. As is shown in Table 2, there are bean c ultures 

 that fall into each category: some are stimulated, some depressed, and 



