Tendrils, Spines and a Fossil Pod in the Greenhouse

Not Every Spike Is the Same

1The greenhouse club at Willow Creek Middle School grows food and garden plants all year: peas and green beans on strings, tomatoes, potatoes in tubs, onions, sweet corn, a potted lemon tree and a barberry shrub by the door. A grapevine and a row of roses grow along the fence outside. This spring, club member Farhan Delacroix made a display about plant parts that do not look like ordinary leaves, such as tendrils that coil around strings and spikes that keep animals from nibbling.

2Ms. Odette Szymanski, the club's adviser, gave Farhan a rule that botanists use. A leaf grows out of a stem, and in the angle just above the spot where the leaf joins the stem there is a bud. That bud can grow into a branch, and flowers grow on stems and branches. So a part that sits in a leaf's place, with a bud in the angle above it, is built from a leaf. A part that grows from the bud above a leaf, or that carries flowers, is built from a stem. A part that grows from the outer skin of the stem, with no bud beside it, is neither.

3Farhan's notes on six parts are in Table 1. He found that parts with the same job are sometimes built from different starting parts, and parts that look very different are sometimes built from the same one.

4Ms. Szymanski explained that scientists compare many features at once, especially features of flowers, seeds and leaf veins, to decide which plants are closely related. A single shared job, like climbing or defense, can be weak evidence, because unrelated plants can solve the same problem in different ways. Features built from the same starting part, in the same pattern, are stronger evidence of a shared ancestor.

5For the second half of the display, Farhan compared the flowers, leaves, seeds and fruits of six crops (Table 2). He added two fossils lent by the county museum. Both come from rock about 50 million years old. One is a twig with net-veined leaves and a seed pod that had split open along two seams. The other is a large fan-shaped leaf with parallel veins.