The Initiation and Growth of Tulip Bulbs

Tulip mother bulbs contain daughter bulbs, and second-generation daughter bulbs are initiated within these daughter bulbs, from February to July. Initiation takes place progressively, the first-initiated bulbs being in the axils of the outermost scales. The innermost second-generation daughter bulbs are finally initiated at the same time as the flower within the daughter bulb. The latest-formed bulbs grow much more rapidly than the others, and soon become larger than the first-formed ones. Later in the season, growth of daughter bulbs falls into three phases, corresponding roughly with autumn, winter, and spring; growth is rapid in autumn and spring, and slower in winter. The rates of daughter bulb growth in the autumn are affected by the amount of suppression by the mother bulb apex, but later these differences disappear. The durations of the phases of growth also vary with the position of the daughter bulb. The outer daughter bulbs grow for a longer time during the autumn phase than the inner ones, so that differences in size due to variation in growth rate are partly nullified. In early spring, all daughter bulbs resume rapid growth simultaneously. Final bulb weight is then approached asymptotically, with the innermost bulbs having the highest weights.