From Seed to Seed:
Plant Science for K-8 Educators
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From Seed to Seed: |
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Adventitious Roots and Shoots Think back to that ivy vine sitting in a jar of water. When we "root" a cutting like that, we're hoping that root tissue will form along the submerged stem. And remember our example of the violet plant? When sprouts form at nodes along the creeping stems, both shoots and roots are produced on the stem tissue. Botanists have a term for this phenomenon. Roots that arise from the stem (or any other non-root tissue) are called adventitious roots. Adventitious shoots, as you might guess, are shoots arising from non-stem tissue, usually roots. Now let's look at some asexual means of propagation and see where adventitious roots and shoots play a role. Asexual propagation by underground structures. Many adaptations for asexual propagation involve underground plant parts. In some cases the structures are true roots, but most are modified underground stems. Most of the underground plant parts that are important in asexual propagation also function as food storage structures. This type of food reserve is especially common among herbaceous plants in temperate regions, whose aboveground parts die back at the end of each growing season. Tubers. Who among us hasn't stored potatoes for too long, or improperly, so 
that the "eyes" begin to sprout? It is unfortunate for the chef, but a great
botany lesson for your students! The common potato isn't a root at all:
it's a tuber-the swollen tip of
an underground stem. The "eyes" on a potato tuber are nodes from which  new
plants, both stems and roots, can sprout. Most gardeners plant "seed potatoes,"
which are pieces of potato (or small whole potatoes) that have at least
two eyes. As the plant grows, it uses the food reserves in the "seed."Production of tubers is one way that a plant can store carbohydrates during the growing season. Then at the end of the growing season, the aboveground portion of the plant dies back. The new tubers overwinter, and sprout again in the spring.
 dahlia.
Tuberous roots can
act as storage structures, allowing the plant to survive a dormant period.
In the spring, the new, adventitious shoot growth uses the food stored in
the roots, and the root shrinks and eventually disintegrates. The plant
produces new tuberous roots each season.Sweet potatoes are usually propagated from slips-adventitious shoots produced when the sweet potato is placed in a moist location. 
Like tubers, tuberous
stems are swollen sections of stem; however, unlike tub  Rhizomes. A
rhizome is an underground stem that grows horizontally at or
just below the soil surface. Rhizomes can be categor  Bulbs. A bulb
is a modified stem that occurs in many familiar monocotyledonous
plants. The bulk of a bulb consists of concentric layers of bulb scales
that enclose the
Plants with bulbs generally reproduce asexually by forming daughter bulbs from buds occurring between the fleshy layers.   Corms. A corm is a swollen leaf base enclosed by dry, scalelike leaves. In contrast to the layered scales of the bulbs, the bulk of a corm is solid, with distinct, if compressed, nodes and internodes. Familiar examples of corm-producing plants are gladiolus and crocus. As with the other structures that we have discussed, corms provide food for emerging shoots. The corm shrinks, and during the growing season another corm is formed at the top of the old one in preparation for the following season.
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ers,
they don't occur at the tips of underground stems. Rather, they occur
on the main stem, often just below the soil level. Tuberous stems generally
have a vertical orientation 
with
vegetative buds produced on the upper end and roots on the lower end.
Examples include tuberous begonia and cyclamen. Unlike tuberous roots,
tuberous stems are perennial, and continue to enlarge every year. If you
have begonias, for example, you can dig up the tuberous stems, store them,
and replant them year after year.
ized
into two types: the thick, fleshy, compressed structure typified by the
iris, and the slender, elongated underground stems of lily-of-the-valley.
Because they are stems, rhizomes have nodes and buds along their length;
new plants can arise at these nodes. Other examples of rhizomatous plants
include bamboo, sugar cane, and many grasses. Quackgrass and poison ivy
are two troublesome plants that spread via rhizomes. 
immature
vegetative or flowering shoot. An onion is an example of a bulb that most
students may have "dissected" in the kitchen. Tulip, 
daffodil,
amaryllis, lily, and hyacinth are some of the more common flowering bulbs.
