LILY STRUCTURE - Lilium Bulbs
Source: NALS Judging Handbook, Letís Grow Lilies
Artwork: Virginia Howie
Starting from below the surface of the soil the lowest organs are the roots. Two types of roots are recognized, basal roots and stem roots. The large basal roots serve the dual purpose of absorbing water and nutrients and also of anchoring the bulb deeper into the ground. The stem roots arise on the stem between the bulb and the surface of the soil and serve primarily to absorb water and nutrients. They, of course, die with the stem each fall. Not all species, e.g. Lilium candidum, produce stem roots.
Next comes the bulb which morphologically is a fleshy underground bud, the scales being the modified bases of leaves, much shortened and thickened, which function as storage organs for food to start off the season's growth. The center of the bulb is called the axis and it is from this structure that the roots and scales arise. When growth starts, the axis develops upward to form the stem.
Three types of bulbs are found among lily species: concentric, rhizomatous, and stoloniferous. In the concentric type, the bulb is essentially globular in shape and the scales are arranged on the base of the axis, called the basal plate.
Bulbs of the concentric type vary greatly among species and hybrids. In some,
the scales are large and loose and are easily broken off in handling. Others are
more firm with the scales held tightly together. The general shape also varies
widely. The color of the bulb scales also varies from white to dark purple
depending upon the variety.
CONCENTRIC (Bulb) . . . Having a common center . . . In this type, new bulbs form within the parent bulb. (Examp. L. tigrinum, L. regale.)
The stoloniferous bulb is common in several American species. Instead of
daughter bulbs developing close to the mother bulb, they are produced on stolons
or runner‑like structures from the axis, often several inches from the mother
bulb. In general, the stoloniferous bulbs have small, tight scales giving a
feeling of firmness.
STOLONIFEROUS (Bulbs) Bulbs which produce new bulbs at the ends of STOLONS. The old bulb eventually dies, while the stolon is left to nourish the new bulb. L. canadense, L. superbum, L. grayi, and L, micbiganense are examples.
STOLONIFORM . . . Applied to lilies whose stems creep underground before emerging. Sometimes one or more smaller (or full size) bulbs will be added before the stem finally emerges. (Examp. L. maximowiczii, L. nepalense.)
The rhizomatous type of bulb is, in general, intermediate between the concentric type and the stoloniferous. The stolons or runner‑like structures are much shorter so that the daughter bulbs more or less form a clump around the mother bulb.
RHIZOMATOUS (BULBS) . . . Perennial, stout, horizontal branching root stock; new bulbs produced as extensions of this rootstalk. (Examp. L. pardalinum, Bellingham Hybrids.)