396 PLANT GROWTH SUBSTANCES 



to normal tissue with respect to gall production when each, respectively, 

 was grafted to healthy plants. 



Tissues of crown-gall origin from a number of species, after cultivation 

 in vitro, when grafted back to healthy plants commonly continue to 

 grow and produce a gall at the graft cite. This was first described by 

 White and Braun (31) for sunflower tissue isolated from secondary 

 crown galls. Such tissue was also grafted successfully to Jerusalem arti- 

 choke plants. The gall tissue itself actually increased in size, the host 

 plant providing a suitable medium and support. This same phenomenon 

 of grafting was successfully demonstrated for the hybrid tobacco tissue 

 (32), for periwinkle (33), and black salsify (9). De Ropp (3,4) carried 

 this study further with some interesting results on the interaction of 

 normal and gall tissue in in vitro grafts. This approach to the role of 

 growth-regulating substances in normal and pathological growth offers 

 some splendid opportunities and deserves further attention. 



The above information provides a general background to the field 

 of plant tissue cultures with special attention directed toward the in- 

 fluence of growth-regulating substances on such cultures. Most of the 

 work has been concerned with cultures derived from normal tissue. 

 A few comparisons were made of the influence of these materials on 

 tissue of normal and pathological origin. Next to be summarized are 

 some phases of the problem studied at Wisconsin. These were concerned 

 with the influences of some representative natural and synthetic growth- 

 regulating substances on tissue cultures from hybrid tobacco and from 

 secondary crown gall on sunflower. The stimulating or inhibiting efl'ects 

 on growth of difl"erent compounds, their critical concentrations and their 

 action on different tissues were investigated. These items were of special 

 interest since the stimulating and inhibiting effects on tissue cultures 

 of sunflower and tobacco of a variety of plant tissue extracts could not 

 be entirely explained on the basis of improved salt balances in the basal 

 media (13,14). 



Influence of concentration of growth-regulatifig substance on iveight of 

 cultures. — The general procedures for culturing plant tissue in vitro were 

 observed. The hybrid tobacco tissue was supplied by P. R. White in 

 December, 194 1. The secondary sunflower crown-gall tissue was isolated 

 in December, 1941, and was free of the inciting bacteria. The basal 

 media were modifications of White's (30) and were described by Hilde- 

 brandt, Riker, and Duggar (14). 



