The Great Plant Escape

Case 5 - Growing Deeper

A dramatic and ideal bulb for class discussion is amaryllis. The bulb is extremely large and after potting will produce a flower in 4-6 weeks. Growth is rapid and will produce a tall flower stem with large blooms. The size of the blooms invites close examination and is excellent to use in the discussion of flower parts, pollination, seed and fruit production. Once the flowers have opened, observe the flower for signs that they are ready for pollination. The prongs of the pistils open upward when the flower is ready to accept pollen. Invite the class to play "bee" and transfer the pollen from the anther to the stigma. A successful pollination results in a swelling of the ovary. When ripe, seeds can be harvested. The same procedure can be done with the paper white narcissus. This whole process illustrates the complete cycle of growth.

There are a number of bulb look-alikes or impostors. Even though they are often called "bulbs," they are botanically different and are actually adaptations of plant parts to fulfill a basic need.

Horizontal stems growing above the soil are called stolons and those growing underground are called rhizomes. Strawberries and spider plants are examples of plants that produce stolons. Iris and quackgrass are examples of plants with rhizomes. From a point on the stolon or rhizome, roots and upright shoots develop. The beauty of this adaptation is that when these stems lie on the soil or just below it, they have no need to spend a lot of energy making strengthening tissue. Thus, they are able to direct all their energy into a burst of rapid, primary growth.

A corm resembles a bulb externally but is very different in structure. Crocus and gladiolus are examples of corms. Corms are short, swollen, underground stems surrounded by the remains of last years leaf tissue. Remove the paper cover and you can see parallel lines. These are the nodes. Cut a corm in half and it is solid in structure and not layered like a true bulb. The growth of leaves and flowers from corms occurs at the expense of the total corm being consumed. New corms form each season on top of the old withered corm.

Tubers are another stem adaptation. Irish potatoes are stem tubers. Stem tubers have "eyes" which are buds. The area between the eyes are the internodes.

Another type of tuber is the root tuber. These are formed on plants like dahlia and sweet potato.

These and other bulb look-alikes can be collected and examined for external and internal differences.

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