STEMS

SO WHAT DO WE ALREADY KNOW?????

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

Stem Basics

1. Stems develop from the embryonic hypocotylhypocotyl

2. We call the stem and the leaves the shootshoot

3. Stems can present a variety of forms some typical some not so much. Consider the stem of a carrot. Where is it????

4. Stems contain the apical meristem.apical meristem. What’s that?What’s that?

a) Shoot apical meristem(b) Leaf primordial

(c) Axillary bud primordium(d) leaf

(e) Stem tissue

Growth of StemsIn 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

pattern2. Lack of Apical Dominance- deliquescent

growth pattern

Apical Dominance or Excurrent Growth

AUXIN!

Apical DominanceExcurrent Growth Pattern

Effects of Pruning

Deliquescent Growth

http://cagle.com/caglecards/main.asp?image=/news/EarthDay10/images/darkow.gif

External Stem Features

External Stem Features

How is a stem ‘put together’?

Function of…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