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Tall peas var. Alaska and dwarf peas var. Progress No. 9 were grafted onto their own roots or reciprocally grafted to determine the rootstock effect on the growth of the stem. In all cases the grafted stems grew the same as their ungrafted controls regardless of which rootstock they were grown on. When similarly grafted plants were supplied with gibberellic acid, good graft unions did not inhibit its translocation. This evidence supports the thesis that the mechanism controlling stem growth in peas is located in the stem and that the roots have no direct control over this mechanism.Since Went (17,18) (6,12,16). Lockhart (10) attempted to demonstrate the controlling aspect of shoot tip-syhthesized gibberellin by grafting a stem from a tall pea onto the root of a dwarf pea. No increased elongation occurred in the stem section of the dwarf rootstock, contrary to expectation, and he concluded that his experiments failed to provide evidence for or against the production of gibberellin in roots or cotyledons.Lockhart (9, 11) suggested that light regulates stem elongation in dwarf pea through some effect, or effects, on the metabolism of gibberellin. He considered three possible mechanisms: (a) light may inhibit the synthesis of endogenous gibberellin, (b) light may cause a destruction or diversion of endogenous gibberellin, or (c) light may make the tissue less responsive to a given amount of gibberellin; and he concluded that visible radiation probably inhibited stem elongation in pea through an effect ' The investigation reported in this paper is in connection with a project of the Kentucky Experiment Station and is published with approval of the Director. on the level of endogenous gibberellin (11). However, Kende and Lang (7) rejected the first two possibilities since they found equal amounts of gibberellin in dark-and light-grown dwarf peas. They favored the third mechanism, that light makes the tissue less responsive. Kohler and Lang (8) produced evidence for substances in higher plants (lima beans) which interfered with the response of dwarf peas to gibberellin, and they suggested that inhibitors may participate in the growth regulation of plants, particularly by an interplay with gibberellins.Our experiments were aimed at finding whether stem growth due to gibberellin is controlled by the root system or stem and/or if an inhibitor is produced in the roots which may be translocated to the stem of the pea plant and in this way regulate stem growth. MATERIALS AND METHODSTwo varieties of peas (Pisum salivum L.) were used: Alaska, a tall pea, and Progress No. 9, a dwarf pea. The Alaska seeds were obtained from a local seed house and the Progress No. 9 seeds from Northrup King, Minneapolis, Minnesota.The seeds were soaked for 5 hr in water and then planted in vermiculite in 3.8-cm pots. The plants were grown in a growth chamber at 20°under continuous illumination. For the first 3 days the plants were watered with distilled water, and after the 3rd day they were supplied daily with Hoagland's nutrient solut...

Comparisons were made of MM.111, MM.106 and EM.IX as rootstocks and ‘Red Delicious’ (RD), MM.106 and EM.IX as 1-, 3-, 5- and 7-inch interstems. The dwarfing effects of the rootstocks were greater than those of the interstems. Interstems reduced the growth of most plant parts in direct proportion to the degree of dwarfing of the interstem and there were few significant differences among plants with different interstem lengths. However, plants with interstems of 1 and 3 inches had higher percentage increases in root weight than those with 5 and 7 inch interstems. Plants with EM.IX interstems showed similar patterns of total plant, leaf and new growth weights. Weight increases of RD interstems were lower than those of MM. 106 and EM.IX interstems. The EM.IX rootstock weights were 101 percent of the weights of the plant tops, whereas rootstock weights were approximately 50 percent of the weights of plant tops for all other treatments.

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