Abstract
Based on the changes of the values of genetic parameters with the growth, the period to select for a character was discussed. The valucs of genetic parameters varied with the growing stage. In root weight, heritability values estimated by variations within type decreased and in root length, those by variations between types increased, as the growth advanced. Therefore, the favourable period to select for root weight was estimated to be during the early growing stage and that for root length to be during the late growing stage.
