Growth of the gynophore of the peanut Arachis hypogaea. 1. Intact and decapitated gynophores

The origin and development of gynophores were studied in a two-seeded, bunch-type peanut ciltivar, Bukene No. 2. Plants were grown and experiments carried out in a greenhouse. An intercalary meristem is formed at the base of the fertilized ovary. When the gynophore is about 6 mm long, it responds positively to gravity, showing sigmoid growth. Marking experiments showed that the meristem extended to 6 mm proximal to the tip of the gynophore, the greatest growth occurring between 2 and 3 mm from the tip. Histoautoradiography showed that the greatest number of labelled nuclei occurred in segment 2; however, because of differences in cell length, the highest proportion of labelled to unlabelled nuclei occurred in segment 3, the region where the greatest overall extension occurred. Both cell division and cell elongation are involved in extension growth. Excision of the ovary resulted in cessation of elongation growth after 4 days or less, together with loss of meristematic features. Removal of the distal half of the ovary was less effective. It is postulated that the developing ovary provides growth factors necessary for maintenance of growth in the intercalary meristem of the gynophore.