The relationship between vascular differentiation and the distribution of ice within Forsythia flower buds

The relationship between vascular development and the distribution of ice within overwintering forsythia flower buds was examined. Previous experiments demonstrated that ice formed in dormant buds within the bud scales, sepals, and in the peduncle and lower portions of the developing flower. The current study demonstrated that these tissues contained columns of primary xylem forming a continuous network with the subtending stem tissues. The vascular traces within the developing petals, anther filaments and pistil were not fully differentiated. Xylem vessels were not present and only procambial cells were observed. Large ice crystals did not accumulate in these tissues. When vascular development resumed in the spring, coincident changes in the distribution of ice within buds were noted. Observations were consistent with the hypothesis that ice propagates into buds via the vascular system, and that the segregation of ice within bud tissues reflects the distribution of xylem.