TABLE III
COMPARISON BETWEEN THE GENERAL PROPERTIES OF THE PHOTOTROPISM OF Avena
AND ITS LIGHT-GROWTH REACTIONS
0
Tip Response
(Optimum Stimulus: Short Exposure;
Low dose)
Base Response
(Optimum Stimulus: Long Exposure;
High dose)
2
H
z
8
i
Properties of the curvature:
Direction and maximum magnitude
Shape
Location of sensitivity
Time course
Change with increasing doses
Properties of the light-growth reaction:
Direction and magnitude
Location of sensitivity
Time course
Change with increasing intensity
Positive, approx. 30°
Concentrated in tip ("tip" curvature)
Tip
Starts slowly (30-40 minutes) near tip,
continues to develop for three hours or
more, migrates basally
Positive, zero, negative, zero
Positive, approx. 18°
Distributed over length ("base" curvature)
Entire plant, especially growing regions
Starts quickly (10-15 minutes) along entire length exposed; reaches complete
development in 90 minutes, then regresses
Increasing positive
Slight depression of growth rate
Tip ("tip" response)
Starts slowly, prolonged
Sharp depression of growth rate
Entire plant, especially subapical ("base"
response)
Starts quickly, reverses, followed by small
acceleration
Depression decreases towards zero (effect
Depression increases to maximum
vanishes)
a
Data of Arisz, Went, van Dillewijn, Haig, and the authors.