The growth and ageing of individual meristems of excised groundsel roots is described. Their behaviour upon repeated subculture is basically similar to that described by other workers for excised tomato roots, although excised groundsel roots require a greater concentration of sucrose for optimal growth than do excised tomato roots. However, growth in low-sugar media can be considerably improved by adding small amounts of 2-naphthoxyacetic acid.
When roots grow vigorously in media containing the optimal sucrose concentration, or in low-sugar media supplemented with 2-naphthoxyacetic acid, they show signs of ageing after a few passages and usually stop growing after about 10 weeks. Roots in low-sugar media grow less vigorously but survive longer, 1-naphthoxyacetic acid is a very effective ‘anti-ageing’ substance in that it enhances survival of roots in high-sugar media, or in media supplemented with 2-naphthoxyacetic acid.
The ageing process appears to be under the control of a hormonal factor which is not β-indolylacetic acid.