ence clearly discernible by taste [45]. When sharing a grapefruit, canny citrus people give the stem-end
half to their companion, retaining the blossom end half for themselves.
In the jungles of southeast Asia where citrus first evolved, all are still green when mature. The ex-
tent to which the expected orange or yellow colors develop depends on the growing area having cold
enough nights to stress the fruits [46]. In subtropical areas such as Florida and Brazil, early varieties may
mature while still green, necessitating postharvest removal of the green chlorophyll with ethylene [47].
B. Pome, e.g., Apple
The typical growth curve of any main crop apple variety is only slightly sigmoidal. Very early varieties,
such as Early Harvest, Yellow Transparent, and Melba, mature to acceptable eating quality before any de-
celeration of growth (Figure 4). Apples that mature this early are very frail and suitable only for local con-
sumption. The longer it takes an apple variety to reach maturation, the more sigmoidal its growth curve.
In general, the later an apple variety matures, the longer its potential marketing life.
Initially, all cells of the apple are alive. Cell division in the epidermis ceases at the end of stage I.
Marked elongation and flattening of the epidermal cells occur throughout stage II, during which period
the epidermal cells extrude waxy, cutinous material. In fully mature late-season apples, the epidermal
cells are separated, dead or dying, embedded in the continuous cuticle (a heterogeneous polymer of fatty
acids overlaid with a layer of wax). The cuticle can continue to develop after harvest. During the stage II
growth period, the epidermis is penetrated by stomata that tend to cork over at full maturity. Under the
epidermis in some varieties is the periderm, a thin layer of cork cambium. If the epidermis is injured early
in stage II growth, as by mechanical abrasion or frost, the periderm develops a protective layer of corky
cells: biologically an excellent protection for the fruit but a “grade-lowering defect” for the packer and
the consumer.
Parenchyma tissue from the fused bases of the calyx, corolla, stamens, and receptacle constitutes the
major part of the edible tissue of the mature fruit. Cell division having ceased at the end of stage I (usu-
152 GRIERSONFigure 4 Increase in the volume of Early Harvest, McIntosh, and Rome Beauty apples from full bloom to
maturity. (From Ref. 37.)