Distribution of dry matter between shoot and storage root of field-grown carrots. III. Development of phloem and xylem parenchyma and cell numbers in the storage root

SummaryThe development of phloem and xylem parenchymatous tissues of the storage root of nine carrot cultivars showed distinctive patterns. There was a much greater proportion of xylem tissue in those cultivars with a greater shoot to root ratio. Thus, Autumn King types, which are generally higher yielding and have larger shoots, had lower phloem to xylem ratio in their storage roots. Collectively these tissues grew primarily as a result of cell division, and variation in root fresh weight between cultivars was closely related to cell numbers. Increase in cell size was of much less importance. The magnitude of the phloem to xylem ratio was also largely determined by cell numbers in these tissues, but differences between cultivars in this characteristic were related to differences in the ratio of mean cell fresh weights. The mean cell fresh weights of phloem varied less between cultivars than those of the xylem. Thus, the latter made a major contribution to these differences between cultivars in the cell weight ratio.