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Abstract

Observations have been made on the root system of groundsel seedlings cultured aseptically in darkness, in media containing sucrose and vitamins. Root development followed a definite pattern, in which loss of meristematie activity occurred first in the primary root and later in the lateral roots. Varying the sucrose concentration of the culture medium modified growth rates considerably but did not change the basic pattern of development. Grovi^th rates were highest, initially, in media containing 4-6 % sucrose but these roots ceased growth much earlier than those in i % and 2 % sucrose. Addition of 2-naphthoxyacetic acid to initially sub-optimal sucrose media stimulated growth but also accelerated the 'death' of the root apex. On the contrary, i-naphthoxyacetic aeid prolonged meristematie activity in high sugar media, resulting in healthy root systems in which the radicle retained its apical dominance. A comparison of the behaviour of seedling roots and excised roots suggests that the pattern of root development in the seedling was controlled by an ageing process similar to that previously observed in excised roots. Discrepancies between the two materials may be attributed to an 'anti-ageing' effect of the shoot.