Agriculture Reference
In-Depth Information
within themselves and form the ovules, two of which occur in each carpel. The
style arises at the apex of the three fused carpels, and is still elongating when
the flower opens (see Fig. 2.17b).
The development of the inflorescence, florets and top-sets in garlic is
shown in Fig. 2.18. Development to anthesis in garlic is rare and, when it can
occur, requires a specific sequence of conditions (see Chapter 4). Usually top-
sets (sometimes termed bulbils) form in the inflorescence and swell to suppress
the florets (see Fig. 2.18E-G). The same can happen in onion, leek and other
species under certain conditions (see Figs 4.35 and 4.41).
The inflorescences of these crops are umbels (see Plate 1). When ripe, the
leafy spathe that encloses the umbel during development splits and the
inflorescence opens. The flower colour and the pattern of opening of individual
flowers within the umbel vary with species (see Table 1.2). Individual flowers
are carried on short stalks (pedicels). In onion, flowers are continuously
carried to the outer boundary of the inflorescence by elongation of the pedicels
before the tepals open. This leads to successive cohorts of flowers opening over
the whole surface of the umbel. In onion there are commonly 200 to 600
flowers per umbel, depending on cultivar, growing conditions and whether the
umbel is formed from the main growing point or an axillary shoot. Similar
umbels containing large numbers of flowers are produced by leeks and
Japanese bunching onions. Chives typically have about 30 flowers per umbel,
rakkyo six to 30 flowers and Chinese chives have approximately 40 white, star-
shaped, fragrant flowers in a flat-topped umbel.
Fig. 2.17.
The development of individual florets. (a) Top view of a young flower in
which primordia of all perianth segments (Iabelled I to VI) and stamens have
differentiated: ipl, inner perianth lobe; ost, outer stamen; ist, inner stamen (
60)
(from Jones and Emsweller, 1936. Courtesy of
Hilgardia
). (b) Open flower with the
inner whorl of anthers shedding pollen. (c) Late in flowering when the stigma is still
sticky and receptive but the tepals and anthers are withering (b and c approx.
2)
(from Currah and Ockenden, 1978. Courtesy of
New Phytologist
).
