Agriculture Reference
In-Depth Information
Fig. 2.18.
Scanning electron photomicrographs of garlic apical and floral
development. (a) Vegetative meristem (vm) with differentiated leaf primordium (lp);
bar = 0.1 mm. (b) Floral transition; the reproductive meristem (rm) is swollen and
hemispherical; the spathe (sp) was removed; bar = 0.1 mm. (c) Differentiation of
flower primordial in a reproductive meristem with spathe removed; first flower
primordia (fp) are initiated in an apex of diameter 0.8 mm; bar = 0.3 mm. (d)
Differentiation within the floral primordial; floral parts are seen in the oldest floral
primordial (fp) while the younger ones still appear as undifferentiated meristematic
domes; bar = 0.4 mm. (e, f and g) Newly developed meristems appear near leaf-like
bracts at the base of the inflorescence; they quickly differentiate and grow to form
small inflorescence bulbs termed top-sets (t); bar = 0.8 mm in E, 1 mm in F and
0.1 mm in G. (a-f from Kamenetsky
et al
., 2004. Courtesy of
Journal of the
American Society for Horticultural Science
; g from Kamenetsky and Rabinowitch,
2001. Courtesy of
Sexual Plant Reproduction.
)
In each flower nectar accumulates in three cups formed between the lower
ovary walls, where the nectaries are located under a small flap, and the broad
bases of the filaments of the inner whorl of stamens. The stages of flower
opening in onion are: (i) opening of the tepals and the beginning of nectar
secretion; (ii) dehiscence and pollen release by the stamens (see Fig. 2.17b);
then (iii) the stigma becomes sticky and receptive when the anthers have
ceased to shed pollen (see Fig. 2.17c).
The development of onion seeds following fertilization is described by
Rabinowitch (1990b) (see also Figs 6.17 and 6.18). Seed size and therefore the
number of seeds per g varies with species; approximate figures are: onion and
Japanese bunching onion, 300; leek, 350; kurrat, 440; chives, 1150. The
