Groivth Substances and Plant Tissue Cultures 



677 



Table 1 . Types of growth response of plant tissue cultures to various concentra- 

 tions of gibberellin. * 



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



for comparative purposes. In view of the results shown in Table 1 as 

 well as similar experiments in this and other laboratories (3, 6, 7, 10), 

 the level chosen was 10 p. p.m. A stimulatory or inhibitory effect at 

 10 p. p.m. indicates the general response of a tissue. However, a lack 

 of response is not conclusive. Broad bean cotyledon is an example 

 of a tissue which is stimulated at a level below 10 p. p.m. At 10 p. p.m. 

 no effect is apparent, yet there is significant stimulation at 0.5 to 5 

 p.p.m. 



The 49 tissues selected for inclusion in this paper represent 17 

 families and 25 species. The cultures came from diverse origins 

 within the plants: pollen, root, stem, leaf, tuber, prop root, cotyle- 

 don, and petiole. The time in culture of these tissues varies from 



Fig. 1. A. The effect of gibberellin on the growth of a tissue culture from avocado 

 cotyledon. Left, untreated; right, 10.0 p.p.m. gibberellin. B. Increased growth of 

 avocado cotyledon tissue culture by removal of 2,4-D from the medium. Left, White's 

 medium with coconut milk; right, the same medium with 6.0 p.p.m. 2,4-D. C. Ne- 

 cessity of 2,4-D for growth of 'Pontiac' potato tuber tissue in culture. Left, White's 

 medium with coconut milk and 6.0 p.p.m. 2,4-D; right, the same medium without 

 2,4-D. 



