394 PLANT GROWTH SUBSTANCES 



rate, nevertheless prevented differentiation under conditions otherwise 

 favorable for it. The higher of these concentrations caused a marked 

 inhibition of growth, but at the lower concentrations the fresh weights 

 were as large and with optimal concentrations even larger than those 

 of the controls. Skoog also found that the cultures produced consider- 

 able quantities of auxin extractable with ether when grown either in a 

 liquid or on a solid medium. 



Bacteria-free tissue cultures of crown-gall origin from a number of 

 species have provided for study important material of a pathological 

 nature. Tissue cultures from primary galls on sunflower (i). periwinkle 

 (33), Paris-daisy (12), black salsify (9), and Jerusalem artichoke (8), and 

 from secondary galls on sunflower (31) and marigold (12) have already 

 received considerable attention. The growth of such tissue in vitro 

 removed the complicating factors that occurred when the gall tissue 

 was studied in the intact plant. A comparison of the influence of growth- 

 regulating substance on tissue of crown-gall origin and of normal tissue 

 indicated some fundamental differences in response to these materials. 

 De Ropp (2), for example, in an interesting study placed fragments of 

 tissue of normal and crown-gall origin from sunflower and periwinkle on 

 media containing indole-3-acetic acid, indolebutyric acid, or a-naph- 

 thaleneacetic acid at concentrations of o.oi and 10 mg. per liter. The low 

 and high concentrations strikingly stimulated growth of normal sun- 

 flower tissue. The low concentration resulted in decreased growth while 

 the high concentration completely inhibited growth of the tissue of 

 crown-gall origin. The high concentration was toxic to normal periwinkle 

 tissues but the low concentration resulted in a slight stimulation. The 

 periwinkle gall tissue was inhibited at the high concentration and un- 

 changed by the low concentration. Furthermore, normal sunflower and 

 periwinkle tissue produced abundant roots at the low concentration and 

 the cambium proliferated at the high concentration. Exposure of the 

 normal sunflower tissue to the high concentration of growth-regulating 

 substance for one day was sufficient to induce root formation. These 

 results with normal tissue were therefore similar to those described 

 by Gautheret (5) for normal tissue of carrot and other species. The 

 sunflower and periwinkle gall tissue showed no structural changes as 

 a result of the growth-regulating substances. 



Gautheret (8) also compared the responses of normal tissue of crown- 

 gall origin of artichoke, lndole-3-acetic acid resulted in progressively 



