I selected links with images and information related closely to the observations described in lab Exercise 5 (Secondary Growth) of your botany lab manual. Preview these resources as you prepare for the laboratory exercise and review these resources as you write your lab reports and study for tests.

Reminder, today's lab begins with a quiz on roots and primary stems.

I. Woody Twigs - Winter Botany

The exercise begins with an examination of woody twigs of deciduous trees gathered in the winter condition (Winter Botany) after the foliage dropped. Characteristics such as the appearance of leaf scars, buds, bud scale scars, and bark permit identification of trees in winter.

You are asked to complete a table in the lab manual to compare twigs of

1. Horsechestnut
2. Maple
3. Sycamore
4. Alianthus
5. Forsythia

I have provided links to illustrate these branches both with and without leaves attached.

II. Key to Woody Twigs in the Winter Condition

In this section of the lab, after examining branches of five different woody species in the winter condition, you construct a simple key that will allow one to distinguish each of the specimens. Expect the quiz on this lab work to include questions that ask you to key out a branch in the winter condition, and also a question that asks you to determine the age of a branch by counting the number of rings of bud scale scars. You may wish to revist lab exercise one which had links to keys and information about keys as well as links to information about a variety of trees.

III. Macroscopic Observations of Secondary Growth and Tissues

In this section of the lab exercise you examine the macroscopic appearance of pieces of woody trees. Materials on display include sections of tree trunks, wood blocks, boards, tree bark and a variety of related materials. Use these specimens and the models of woody stems and the wall charts and diagrams from reference books to clarify the cuts (tran>

---

Transfer interrupted!

radial and tangential) of wood.

Be sure you can recognize and identify bark, wood, vascular cambium, heartwood, sapwood; annual rings, spring wood, summer wood, rays, pores, knots and other macroscopic features. I have provided links to illustrations of wood blocks.
 
 

IV. Microscopic Observations - Vascular Cambium and 2^o Tissues

After you understand the macroscopic features of woody plants, move on and examine microscopically the thin sections of young woody twigs. Especially when young, much that you see should be very similar to the primary stem tissues that you examined last week. Usually it is fairly easy to recognize the pith in the center and the cortex near the outside in these transverse sections of young stems.

Depending on the age of the woody stem, the epidermis may be present and intact, present and disrupted, or lost, perhaps along with some of the cortex. Often fibers of the bundle cap still mark the outer boundry of the primary phloem clearly. The primary xylem will be the innermost xylem, and it is often appears fairly distinct as it protrudes into the pith.

If you compare twigs that are 1 year old with those that are 2 and 3 years old, you can see a progressive increase in size as additional annual rings of xylem are added. Note also, the outer tissues becoming compressed, disrupted, and eventually lost.

 Slide of sections of twigs of Tilia, Oak, Pine and several other woody species are available for study. I have provided links to many illustrations of sections of woody twigs.

 After you feel comfortable locating the primary and secondary tissues in transverse sections of young stems, examine in detail wood (secondary xylem) sectioned in transverse, radial and tangential cuts. Compare the appearance of these cuts in Oak (hardwood) and Pine (softwood). Learn to recognize the kind of section (note especially the appearance of the rays) Focus your attention on identifying tissues by their location, cell types and characteristic appearance. Visualize how sections of stems would be positioned in the intact stem, and try to relate transverse (c.s.) with longitidinal (radial and tangential) sections. Learn to distinguish between (1) hardwoods and softwoods, (2) transverse, radial and tangential sections. I have provided links to illustrations of sections of wood and the appearance of cells types.

V. Microscopic Observations - Cork Cambium and Periderm

The cork cambium is the second kind of secondary meristem. Cork cambia often are produced initially in the cortex or epidermis, but in older woody trees in which epidermis and cortex are lost, cork cambia may be produced repeatedly in the secondary phloem. Examine the cork cambium, cork and cork parenchyma which make up the layers of the periderm in the slides on display, including Geranium, and lenticel of Sambucus.

General Information

I will introduce each of the three sections of the lab exercise 1) winter twigs; 2) logs, cuts of wood, bark; 3) tissues and cell types,and then allow you to work mostly on your own in this lab period. As usual, I will be available to work with you individually and to help you locate or interpret any of the structures mentioned in the laboratory exercise. Also, I will have labeled transparencies and labeled diagrams from reference books available to assist you in learning to identify tissues and cell types.

As you review today's observations in preparation for the lab quiz, consider the following potential quiz items.

1. Key out a woody twig
2. Determine the age of a woody branch by counting rings of bud scale scars
3. Determine the age of x.s. of woody stem by counting annual rings
4. Locate orientation of "center of tree" by relative position of spring and summer wood
5. Distinguish transverse, radial and tangential cuts (based largely on apparance of rays)
6. Distinguish between nonporous, ring porous and diffuse porous woods
7. Distinguish between hardwood (they have tracheids, vessels and fibers) and softwood (tracheids)
8. Be able to identify cell types (ray initial, tracheid, vessel, etc.)

    Assignment for Laboratory Exercise 5  2^o Growth and Woody Stems

1.   Examine the materials on display in the room. These will
     include tree trunks, samples of bark and wood, preserved
     specimens, wall charts, stereo models of stems, microscope
     slides, photographs and electron micrographs of woody stems.

2.   Label Figure 5.1 Woody Twig.

3.   Sketch vegetative and flowering buds of Lilac or Forsythia

4.   Complete the key to plants in the winter condition.

5.   Label Figure 5.2 Woody Stem and answer the questions in part
     III based on the woody stems you observe.

6.   Examine transverse sections of young woody stems of hardwood
     and softwood species and label Figures 5.5 and 5.6.

7.   Sketch representative xylem cell types in Table 5.2 Xylem
     Cell Types

8.  Examine transverse, tangential and radial sections of wood
     of a hardwood and softwood species. Label Figure 5.7.

9.  Prepare for a quiz in two weeks.