INTERNODE ELONGATION IN XANTHIUM PLANTS TREATED WITH GIBBERELLIC ACID PRESENTED IN TERMS OF RELATIVE ELEMENTAL RATES

Xanthium plants were grown vegetatively and their developmental stages were designated by a previously described plastochron index (PI). Internodes of plants, both treated with gibberellic acid (GA 3 ) and untreated, were marked with India ink and photographed during 3 successive days. The relative elemental rates of elongation d(dX/dt)/dX were estimated between 15.7 and 19.0 plastochrons. The rate of growth of the GA 3 ‐treated internodes was at least twice that of the control. The emerging pattern of acropetal internode elongation was similar in both GA 3 ‐treated and control plants. Only rates of growth were significantly higher in the GA 3 ‐treated plants. The acropetal pattern of internode elongation was the opposite of the basipetal pattern observed in Xanthium leaves but followed the acropetal pattern observed in Helianthus and Phaseolus internode growth.