Some recent results on growth stresses in trees

Abstracts

486

6. ZOOLOGY/BOTANY

STRESS IN THE CONTROL OF PLANT GROWTH AND DEVELOPMENT

THE ROLE OF MECHANICAL

PHILIP M. LINTILHAC

(Department

of Botany, The University of Vermont, Burlington, VT)

What is the relationship between mechanical stress, the cellular architecture of a growing tissue, and the final form assumed by the growing plant? We propose that mechanical stress, through its ability to control the orientation of newly installed cell walls in actively growing regions of plant tissues, can serve as a special kind of developmental information which provides a link between the succession of forms which is the vegetative lifehistory of the plant. We have investigated the relationship between stress and cellular structure by using a simple home-made photoelastic technique capable ofgenerating a complete mapping of the lines of principal stress from a 2-dimensional gelatin or plastic model. Our results are compared with sectioned material showing cell wall patterns in actively growing plant tissues. FEEDING M.

AT LOW REYNOLDS

A. R. KOEHL (Department

NUMBER:

PARTICLE

CAPTURE BY COPEPODS

of Zoology, University of California, Berkeley, CA)

Although calanoid copepods are abundant planktonic crustaceans that play a major role in the transfer ofenergy through marine food chains, their feeding mechanisms have been poorly understood. High-speed movies (made with J. R. Strickler) of dye streams around feeding Eucalanus pileatus revealed how these important herbivores move water to capture food. These tiny animals, whose feeding appendages beat at 20Hz and operate at maximum Reynolds numbers of only 2 x lo-* to 2 x lo-‘, live in a world dominated by viscous forces. These copepods propel water past themselves by a complex series of appendage movements and actively capture parcels of water that contain food particles. SOME RECENT

RESULTS ON GROWTH STRESSES IN TREES

ROBERTR. ARCHER(Department

of Civil Engineering, University of Massachusetts, Amherst, MA)

Regular patterns of growth strains develop in growing woody plants and trees. Over many years of growth, large internal residual stresses build up. Continuum models can predict these stress distributions. Growth strains are modified in certain cases to cause stem reorientation and branch movements by changes in the structure of the cell wall.

C. MECHANICAL

STRESS RELAXATIOS ,ARTHUR MELVIN

DEAN CUTLER*,

PROPERTIES

IN CONNECTIVE RICHARD

OF TISSUES

TISSUE OF CHICKENS WITH SCOLlOSlS

S. RIcGI%t, HUNG-JYNG Lwt, DANIEL R.

BENSON+,

R. RAMEY*, LEOSARD R. HERRMAN*, ROBERT B. RUCKER: and URSCLA

(Departments

of *Engineering, University

K. ABBOTTF and BAvian Science, torthopaedic Surgery, +Nutrition + of California at Davis, Davis, CA)

The mechanical properties of the spinal ligaments and tendons of chickens which develop idiopathic scoliosis were studied in stress relaxation experiments. The material from the chickens with scoliosis, when held at a fixed deformation, showed a more rapid and greater reduction in force required to maintain this deformation than did material from the control chickens. This mechanical abnormality could contribute to the spinal curvature. STRAIN MEASUREMENT JOHN BOYLE,

IN THE MEDIAL COLLATERAL

and MALCOLM Burlington, VT)

STEVEN: ARMS, ROBERT JOHNSON

POPE

LICAMEST

(University of Vermont,

Evaluation and treatment of injuries to the medial collateral ligament (MCL) require a knowledge of its strain characteristics. This study intends to ‘map’ absolute strain in the MCL as a function of joint position and force application. We have developed a transducer capable of detecting displacements of 0.001”. It is tiny and has minimal influence on ligament bahavior. Studies have been conducted on the MCL of amputation specimens. Each knee was subjected to a range of motion and abduction forces with simultaneous recording ofjoint angle. A ligament strain ‘map’ was obtained.