matous tissue consists of large, thin-walled cells with a surprising volume, estimated at ca. 25%, taken up
by airspaces [37].
Comment on the Relation Between Fruit Structure and Handling Damage. Because most
apples have a continuous cuticle, they are very resistant to water damage and have even been stored suc-
cessfully under water. If fungal spores enter through a break in the cuticle, fungal hyphae tend to spread
so slowly that it is common to cut out an infected area and consume the rest of the apple. However, ap-
ples and pears have very little resistance to pressure, which can rupture parenchymatous cells. These are
rich in oxidases and surrounded by air in the intercellular interstices. The results is an ugly dark brown
bruise.
Because of its discontinuous waxy coat and occasional still-dividing epidermal cells [38], a citrus
fruit has poor resistance to prolonged submersion in water. The structure of a citrus fruit, with its spongy
albedo and radially oriented juice sacs, is very resistant to pressure from smooth surfaces. It does not
bruise but is very susceptible to damage from sharp objects. Any rupture of epidermal oil cells releases
“peel oil,” toxic to adjacent tissue, with resultant ugly lesions (“oleocellosis”). Any fungal spores intro-
duced into the albedo find a perfect culture medium. The spread of fungal mycelium is almost explosive.
- Banana (Musa sapientum)
An interesting tropical fruit, the banana, is sometimes classified as a berry, which is clearly erroneous be-
cause nonovary tissue is involved (be it only as the nonedible skin of the fully mature fruit). Banana flow-
ers are dioecious, the male flowers being borne within conspicuous purple bracts at the end of the long,
hanging inflorescence. The female flowers are clustered in groups along the stem of the inflorescence.
These groups of flowers develop into clusters of fruits called “hands,” in which each individual fruit is re-
ferred to as a “finger.” The general tendency is that the more hands there are on a bunch, the more fingers
there are in each hand.
The female flower is inconspicuous and described as a “tepal,” in which the components of the pe-
rianth are so similar in size, form, and coloration that sepals cannot be distinguished from petals [1]. The
inconspicuous perianth is abscised immediately after the flower opens. Thus only ovary and receptacle
remain.
Pollination is necessary for fruit set, but all commercial varieties are, nevertheless, parthenocarpic.
Banana breeders thus have a double problem. When, for example, Panama disease was wiping out Gros
Michel, the major commercial variety of Central America, they had to cross-fertilize with seedy resistant
varieties. With that accomplished, backcrossing was necessary to eliminate the seeds while retaining nec-
essary disease resistance. This was accomplished in a surprisingly short time.
Initially, the peel (which is receptacle tissue) weighs five times as much as the interior pulp. As the
fruit grows, the endocarp develops fleshy protrusions into the locules forming the edible pulp. At full ma-
turity, the edible pulp typically weighs twice as much as the inedible peel. However, few commercial ba-
nanas are allowed to reach full maturity. For long-distance shipment, bananas are picked at stages of de-
velopment known by such terms as “^34 -full” and “^23 -full,” terms describing a somewhat angular cross
section. Fortunately, the highly climacteric banana will ripen to good eating quality even when harvested
well short of physiological maturity. It is usual commercial practice for bananas to be shipped green and
ripened in “ethylene degreening rooms” at destination. In addition to accelerating the natural climacteric
ripening process, this ensures uniformity in ripening, a convenience in marketing.
D. Aggregate Fruits
Aggregate fruits are compound fruits produced from many pistils in an inflorescence rather than from a
single pistil. Temperate-zone aggregate fruits include strawberry, mulberry, and the various cane and
bramble fruits. As mentioned previously, the fig is an aggregate fruit, with its minuscule flowers inside
the vaselike receptacle and so indiscernible without dissection of the fruit. Among tropical fruits, bread-
fruit, pineapple, and cherimoya are aggregate fruits. Three familiar examples of aggregate fruit are dis-
cussed here.
- Raspberry (Rubus idaeus)
The raspberry is an intrinsically frail fruit in that, unlike its near relative the blackberry, at picking the re-
ceptacle remains on the plant. The harvested fruit is thus hollow, formed only from adhering drupelets
FRUIT DEVELOPMENT, MATURATION, AND RIPENING 149