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Bulbs are a primary example of a group of plants called geophytes that produce specialized under-ground structures that function as storage organs and permit the plant to survive adverse conditions.

Geophytes include bulbs, corms, tubers, tuberous roots, tuberous stems, and rhizomes.

These are often lumped together as flowering bulbs by gardeners, but each of these geophytes has a distinctive anatomy that impacts its propagation.

Photo of a bulb.

A bulb is a specialized underground organ consisting of a short, fleshy, stem axis (basal plate), bearing at its apex a growing point or a flower primordium enclosed by thick fleshy scales.

Bulbs are mostly produced by monocots. Most of the bulb consists of bud scales that act as reserve food storage while the bulb is dormant.

In the center of the bulb is either a vegetative or flower meristem.

Illustration of a bulb cross-section with multiple parts identified. Parts illustrated are: tunic (outer bulb scale), main lateral bulblet, basal plate, adventitious roots, flower bud, foliage leaves, bulb scales, and lateral bulblets.

There are two types of bulbs - Tunicate or Non-tunicate.

Photo of a hyacinth bulb as an example of a tunicate bulb.

Photo fo a lily bulb as an example of a non-tunicate bulb.

Tunicate (laminate) bulbs have an outer layer of bulb scales that are dry and papery.

This covering provides protection from drying and mechanical injury to the bulb.

The inner bulb scales are fleshy and give the bulb its solid feel.

Photo of an assortment of popular tunicate bulbs, showing flowering onion, hyacinth, tulip, daffodil, and iris.

An assortment of popular tunicate bulbs.

Tulip is a common example of a tunicate bulb.

It has a papery outer layer covering the storage scales tightly appressed to each other.

The main stem with the leaves and flower emerges through the center of the bulb.

Note the offsets (arrow) developing from the basal plate at the bottom of the bulb.

Photo of two tulip bulbs, one with tunic entact, and the other with it removed, and an arrow identifying offsets.

Non-tunicate or scaly bulbs lack the papery tunicate found in tunicate bulbs like tulip.

The non-tunicate bulb consists of separate "scales" attached at the basal plate.

Illustration of non-tunicate bulbs, the first whole, the second a cross section. The cross section has multiple parts identified: leaves, basal plate, flowering shoot of mother bulb (past season), new daughter scales (next season), old mother scales (past season), growing point of daughter bulb for next season flower, and contractile basal roots.

In general, non-tunicate bulbs are easily damage and must be handled more carefully than tunicate bulbs.

Scales are modified leaves and these can be removed and handled as leaf cuttings where they form new bulbs at the cut surface of the scale.

Photo of a lily non-tunicate bulb.

Lily

Lily bulbs display two types of root systems. Adventitious roots develop from the new stem and act to absorb water and nutrients.

Contractile roots develop from the base of the bulb. Contractile roots function to readjust the depth of the bulb in the soil.

By shrinking and expanding the contractile roots pull the bulb to the proper depth in the soil.

Photo of a lily bulb with the two elements pointed out; the fleshy contractile roots, and the fibrous adventitious roots, which will form along the emerging stem.