680 



L. G. Nickell and W. R. Tulecke 



rather recent isolates to tissues which have been maintained in vitro 

 for 15 years. The media used include both synthetic and supple- 

 mented types. The methods of induction that led to the establish- 

 ment of these strains include hormonal, crown gall, virus, and genetic. 



The results of a large number of experiments incorporating 10 

 p.p.m. of gibberellin in the nutrient media are shown in Table 2. 

 These show that, while a few tissues are increased in their growth and 

 others show no response, the majority are retarded. For example, 

 all three strains of rose tissue w^ere retarded; avocado cotyledon and 

 the pigmented cactus stem crown gall were killed. 



The five strains of tissue from monocotyledonous species were 

 either reduced or showed no effect. These strains are from three dif- 

 ferent families and represent leaf, seedling, and root cultures. 



Severe depression of tissue growth was noted for two crown-gall 

 tissues of sunflower, one from the stem and the other from the petiole. 

 Growth values at 10 p.p.m. gibberellin were approximately one-half 

 the control values. The results of five experiments with petiolar 

 crown-gall tissue of sunflower are presented in Table 3. Variations 

 in growth among these experiments are due principally to differences 

 in the physiological state of the inocula. Nevertheless, the response 

 obtained, in this case depression, is consistent. Of the other crown- 

 gall tissues tested, some were depressed (Vinca and Melilotus stem). 

 Only two were stimulated to any appreciable extent (Melilotus root 

 crown gall, white and differentiated), and these responses were not 

 so striking as the depressions. 



Growth of three strains of tissue from the Leguminosae was in- 

 creased by gibberellin; Vicia faba (broad bean) cotyledon tissue was 



Table 3. The variation in growth of Helianthus petiole crown-gall tissue between 

 experiments. All experiments run for 4 weeks on LP medium. 



* Ratio ul Iicsh weight at end of test over initial fresh weight. 



