Studies on the rosette plant Hieracium floribundum.: I. Observations related to flowering and axillary bud development

Abstract

Hieracium floribundum is a rosette species requiring a number of long days for flower induction. Histological studies of vegetative, transition, and floral apices showed the structural changes associated with flower induction in this species. One striking histochemical change observed was the absence of starch in vegetative apices and the accumulation and retention of quantities of starch in prefloral and floral apices. A study of initiation and development of axillary buds at the time of flowering revealed that there was a gradient in the potential to flower shown by these buds along the developing flower stalk to the base of the plant. The buds in the axils of upper peduncle bracts always develop as capitula while the apices of the buds in the axils of the next few bracts assume the shape of floral buds but fail to develop unless the upper developing inflorescences are removed. Buds in the axils of the lowest bracts and upper (youngest) leaves have the potential to form rosettes, stolons, or inflorescences depending on the environmental conditions in which the plants are grown. Buds formed in the lower (oldest) leaf axils normally fail to grow out until after seed set when a few may develop as rosettes. Possible explanations for these results are discussed, and some experimental approaches being used to elucidate the physiological basis for bud expression are indicated.