THE GROWTH CAPACITY OF THE SUNFLOWER HYPOCOTYL

Abstract

Capacity for elongation was localized mainly in the 10 mm. of the hypocotyl immediately below the point of attachment of the cotyldedons. This capacity was enhanced both by inoculation the fragment with crown-gall bacteria and by culturing the fragment in the presence of 0.01 mg./l. IAA. Fragments from the upper region of the hypocotyl, when cultured on sucrose and mineral agar, had a smaller capacity for growth in breadth and in fresh and dry wt. than had those taken from the lower regions. This difference was eliminated when 1.0 or 0.1 mg./l of IAA was present in the medium. Inoculation with crown-gall bacteria also largely eliminated these differences. Capacity for production of adventitious roots was lowest in fragments taken from the upper 10 mm. of the hypocotyl. Root production by these fragments was enhanced by the presence of 0.1 mg./l. IAA in the medium but still remained less than that of fragments from the central region grown on a similar medium. Inoculation with crown-gall bacteria also enhanced root production. Fragments from the extreme base of the hypocotyl developed fewer roots than did fragments from the central region. Capacity for tumor production in response to inoculations with crown-gall bacteria was about equal in all fragments.