Juvenile Stage in Cultivated Forms of Brassica oleracea

Abstract

Stokes and Verkerk1 showed that while chilling induces flowering in Brussels sprouts, there was a juvenile stage during which chilling was ineffective. This is reflected in the horticultural practice of overwintering small seedlings derived from an August sowing of Brussels sprouts, which then grow vegetatively for a whole season without flowering. A similar procedure is successfully followed in the cultivation of spring and some autumn and cattle cabbage, suggesting the existence of a juvenile stage in these also, as if the plants, as a result of a too early sowing, are too large (that is, beyond the juvenile stage); winter chilling induces premature flowering (bolting) in the following spring2,3. I have, from August sowings, successfully overwintered outside, seedlings of autumn and winter cabbage (3 cultivars), kale (cottagers, hearting, marrow stem and thousand-headed), kohl rabi (4 cultivars), sprouting broccoli (2 white and 2 purple cultivars) and heading winter cauliflower or broccoli (9 cultivars), as well as those of spring cabbage. With all these cultivated forms a high proportion have, when transplanted to permanent quarters either in the October or April following sowing, continued to grow vegetatively, whereas plants from a July sowing all flowered in the spring following. This experience suggests that in all these cultivated types a juvenile stage exists during which chilling in ineffective in inducing flowering.