Agriculture Reference
In-Depth Information
Fig. 2.9.
Leaf initiation and early development at the onion shoot apex. (i) The
earliest visible stage of leaf development; the new leaf appears as a crescent-shaped
ridge (c) to one side of the shoot apex (e). (ii) The new leaf blade (c) begins to
overgrow the apex (e). (iii) The sheath (b), as well as the blade (c), overgrow the
apex (e). (iv) One side (c) has clearly formed a blade while the opposite side (b)
completes the tubular sheath, with the tip (t) of a younger leaf visible through the
pore at the junction of sheath and blade. (v) Transverse section of apical region. A
and D, C and B and a and d are, respectively, the blade and sheath sides of
successively younger leaves (from Hoffman, 1933. Courtesy of
Botanical Gazette
).
Fig. 2.10.
Median longitudinal section through the stem (baseplate) of a 3-month-
old onion seedling, showing a root initiating beyond the periphery of the layer of
dividing cells, termed the primary thickening meristem (PTM), which causes the
stem to grow in width (from de Mason, 1979. Courtesy of
Botanical Gazette
).
