STEMS

SO WHAT DO WE ALREADY KNOW?????

Stems exist for three reasons To produce leaves, branches and flowers To hold leaves up to the sunlight To transport substances between roots

Stem Basics hypocotyl 1. Stems develop from the embryonic hypocotyl shoot 2. We call the stem and the leaves the shoot 3. Stems can present a variety of forms some typical some not so much. Consider the stem of a carrot. Where is it???? apical meristem. What’s that? 4. Stems contain the apical meristem. What’s that?

a) Shoot apical meristem (b) Leaf primordial (c) Axillary bud primordium (d) leaf (e) Stem tissue

Growth of Stems In the spring, the shoot lengthens rapidly from the elongation of cells below the apex similar to the “extension of a telescope” Will produce two patterns of growth in stems 1.Apical Dominance- excurrent growth pattern 2.Lack of Apical Dominance- deliquescent growth pattern

Apical Dominance or Excurrent Growth AUXIN!

Apical Dominance Excurrent Growth Pattern

Effects of Pruning

Deliquescent Growth

External Stem Features

How is a stem ‘put together’?

Function of… Cork- Cortex- Phloem- Vascular cambium- Xylem- Pith-

DENDROCHRONOLOGY

Dendron= tree + Chronos= time + Logos= word= the study of _____________________ DENDROCHRONOLOGY

DEPENDENT ON THE PRINCIPLE OF “UNIFORMITY IN THE ORDER OF NATURE” OR The concept that the present is the key to the past.

but it’s a whole lot more than that… DENDROARCHAEOLOGY- uses tree rings to date when timber was felled, transported, processed or used for construction of wooden artifacts DENDROCLIMATOLOGY- uses tree rings to study climate and reconstruct past climate DENDROECOLOGY- uses tree rings to study factors that affect earth’s ecosystems AND AT LEAST 5 MORE “DENDROS”

SEAHENGE at Holme-next-the-Sea

WHY RINGS??? EARLY IN THE GROWING SEASON TREES PRODUCE THIN-WALLED CELLS REFERRED TO AS SPRINGWOOD OR EARLYWOOD. LATER IN THE GROWING SEASON WHEN CONDITIONS ARE LESS THAN OPTIMUM, TREES PRODUCE THICKER-WALLED CELLS CALLED SUMMERWOOD ORLATEWOOD. TOGETHER, THESE MAKE WHAT WE REFER TO AS AN ANNUAL RING.

Factors that affect the appearance of annual rings include the following. RAINFALL PHYSIOLOGY SLOPE GRADIENT SUN WIND SOIL PROPERTIES TEMPERATURE SNOW ACCUMULATION

Annual Rings can be compared and matched with trees growing in the same geographical zone and under similar climatic conditions to produce CHRONOLOGIES.

The Increment Borer

CHRONOLOGIES The Bristlecone Pine which can live for thousands of years has produced tree ring records that travel 9000 years into the past. River Oaks growing near the Main and Rhine Rivers provide records from over 10,000 years ago