Horticulture Principles and Practices

FIGURE 3–7 Rhizomes. These
underground structures differ in
size and may be significant storage
organs of the plant where
they are thick, as in ginger
(Zingiber officinale).
Rhizome
Leaf
Rhizome
(a) Thick rhizome
(b) Thin rhizome
Apical bud
Papery covering
(tunic)
Stem tissue
Roots
Roots
(a) Whole corm
FIGURE 3–8 A corm. (Source: George Acquaah)
(b) Vertical section
(c) Whole corm
Tunic
Roots
Scale
Flower bud
Tunic
Basal plate
Roots
(a) Whole bulb
(b) Vertical section
(c) Section of whole bulb
FIGURE 3–9
Tunicate bulb.
74 Chapter 3 Plant Anatomy
structure called a bulb. These scale leaves store food. Plants including tulip, lily,
onion, and hyacinth produce bulbs. Unlike corms, bulbs lack distinct nodes and
internodes. There are two basic types of bulbs. A bulb is described as tunicate (as
in onion) when the modified leaves completely cover the stem in concentric layers
with addtional protective tunic that dries up into a relatively thin membrane upon
harvesting. Bulbs like iris, tulip, and hyacinth are described as cold-hardy and
planted in the fall season to flower in springtime. Others like Amarylis and
Hymerocallis are tender bulbs that are planted in summer. Bulbs produce side
branches called bulblets or offsets that are used as propagules (Figure 3–9). In
Easter lily, the attachment of the leaves is only partial, not concentric, and
irregular. This type of bulb is called a scaly bulb and lacks a protective tunic. They
are more prone to damage and dessication (Figure 3–10).