676 L. G. Nickell and W. R. Tulecke 



justed, and the solutions sterile-filtered through sintered glass. The 

 amount necessary to give the desired level was added to the auto- 

 claved agar medium just before solidification. Recent results in our 

 laboratory, however, indicate a surprising stability of this mixture to 

 heat. Only about one-third of the activity was lost after autoclaving 

 for 15 min. at 15 lbs. pressure. The activity was measured in the 

 dwarf pea test and with avocado tissue. 



Media 



Three synthetic media (White's, LP, and 24) and modifications of 

 each were used to grow the varied types of tissues included in these 

 tests. The medium (20 ml.) was added to 1 X 6 in. Pyrex test tubes, 

 plugged with nonabsorbent cotton, and sterilized by autoclaving for 

 15 min. at 15 lbs. pressure. The pH level of all media was adjusted 

 to between 5.0 and 6.0 before autoclaving. 



For many tissues the media were supplemented by 2,4-D (6 p.p.m.) 

 and coconut milk (18 per cent by volume). The coconut milk added 

 to culture media is prepared by collecting the liquid from 100 mature 

 coconuts. This pooled coconut milk is filtered, dispensed into flasks, 

 autoclaved, and stored at 5° C. Before use, it is filtered to remove 

 precipitated protein. In this processed form it is then added to media 

 at 18 ml. per 100 ml. of medium, and re-autoclaved. 



Tissue Culture Methods and Experimental Conditions 



The inoculum for each test level was weighed and divided into 

 5 tubes. The final w^et weight in the 5 tubes was divided by the inoc- 

 ulum wet weight to give an index of growth, termed the "growth 

 value." This is the only term used in the present investigation to ex- 

 press increments of growth. Growth was in an air-conditioned cul- 

 ture room at 21° C. in diffuse light. 



EXPERIMENTAL RESULTS 



Dosage-response experiments were set up with gibberellin levels 

 varying from 0.1 p.p.m. to 100 p.p.m., using several different kinds of 

 tissues. The responses of the 4 tissues selected for this study were either 

 stimulatory or depressive (Table 1). The Riimcx (sorrel) virus tumor 

 tissue was stimulated at 10 p.p.m., while the broad bean cotyledon 

 tissue was stimulated from 0.5 to 5 p.p.m. Taxus pollen tissue was 

 slightly depressed at 10 p.p.m., strongly at 100 p.p.m. Avocado cotyle- 

 don tissue was extremely sensitive, being strongly inhibited at 5 p.p.m., 

 and killed at 10 p.p.m. (Figure lA). 



Because of the large number of tissues to be evaluated in the pres- 

 ent work, it was necessary to decide on one test level of gibberellin 



