TEACHER GUIDE

TOPICS:  Plant classification, plant structure

LEVEL:  High school

TIME:  One class period

ADVANCE PREPARATION:  Collect twig samples of common evergreen and deciduous trees and label each species with an identifying letter written on masking tape tabs.  You may prefer to have students bring in the samples, take the class on a field trip to collect samples, or take the keys outdoors for direct species identification .

MATERIALS: Select key(s) and number of species at the difficulty level most appropriate for your students.  The northeastern and western versions of the "Key to Selected Winter Twigs" include only the most common conifer and deciduous trees, and are easier to use.  If this key is used, ten to fifteen species are recommended.  The complete keys ("Winter Key to the Genera of Northern Conifer Trees" and "Winter Key to the Genera of Northern Deciduous Trees") include all native trees for use by more advanced students.  Collect fewer twig samples for identification if the complete keys are used.

QUESTIONS:

1. Evergreen trees, such as pine, spruce and hemlock, retain their needles all year long, and produce their seeds in cones.  Deciduous trees, such as beech, oak, and maple, shed their leaves, and produce their seeds in flowers .

2. The tamarack (larch) is a conifer that sheds its needles in autumn .

3. Different genera of conifers can be distinguished by the shape, size, attachment, and arrangement (ranking) of the needles .

4. Different species of pines can be distinguished by the number of needles per cluster, their length, and color .

5. Deciduous species can be distinguished by bud characteristics, the shape and arrangement of their leaf scars, color and texture of the bark, etc .

6. Maple, ash, dogwood, and horse chestnut have opposite leaf arrangement.  You can remember these species using the mnemonic phrase "MAD Horse" .

7. Terminal buds are at the ends of branches; axillary buds are located above the leaf scars .

8. Bud scales protect the growing tip of the stem .

9. Lenticels allow gas exchange through the stem .

10. To determine the age of a woody twig, count the number of rings of bud scars, or the number of annual rings seen in cross-section.