10
DAVID M. GATES
incident radiation and its temperature is under strong influence by the
radiation.
Many organisms can control the amount of area presented to the
various sources of radiation by flattening the body, extending appendages, or simply by means of orientation. Leaves may wilt and change
the angle to the direct sunlight and some plants are heliotropic. Furthermore, most plants with their leaves more or lees fixed in direction change
the area presented to the sun as the sun moves with respect to the
earth's surface during the day.
The term, Qra, represents the energy emitted as longwave, infrared,
thermal radiation according to the fourth power of the surface absolute
temperature, Ts, in O K with an emissivity e. Hence,
Qrsa = c 0 T ~ ~
(4)
where ( I = 8-13 x lo-" cal cm-* "K-'min- The emissivity, E, of most
animal and plant surfaces for the far infrared is 0.96 to 0.97. "here are
exceptions where the emisaivity is as low as 0.90 or leas.
B. CONDUCTION COEFFICIENT
If the organism is in physical contact with a surface at temperature,
Tg, such as ground, rock, or tree trunk then energy is exchanged by
conduction. If the underlying surface is cooler than the organism, energy
is conducted from the organism into the substrate and if warmer than
the organism the underlying substrate will deliver heat to the organism.
For many animals this term is often of considerable significance. For
plant leaves the only possible conduction is into or out of the stem and
is usually negligible. The amount of heat conducted per unit area is
proportional to the temperature difference T, - To and to the conductivity, k, of the material. Hence,
Qcond = &Ts - T I )
(5)
The conductivity is the coupling factor between substrate and organism
temperature$.
c. CONVECTION COEFFICIENT
For organisms in air or in water, energy is exchanged by convection
in which molecular d i h i o n of heat occurs in the adhering boundary
layer at the organism surface and then mms movement occurs in the
fluid beyond the boundary layer.
1. 8tiU Air
Masa movement will occur in the case of natural conveotion due to
DAVID M. GATES
incident radiation and its temperature is under strong influence by the
radiation.
Many organisms can control the amount of area presented to the
various sources of radiation by flattening the body, extending appendages, or simply by means of orientation. Leaves may wilt and change
the angle to the direct sunlight and some plants are heliotropic. Furthermore, most plants with their leaves more or lees fixed in direction change
the area presented to the sun as the sun moves with respect to the
earth's surface during the day.
The term, Qra, represents the energy emitted as longwave, infrared,
thermal radiation according to the fourth power of the surface absolute
temperature, Ts, in O K with an emissivity e. Hence,
Qrsa = c 0 T ~ ~
(4)
where ( I = 8-13 x lo-" cal cm-* "K-'min- The emissivity, E, of most
animal and plant surfaces for the far infrared is 0.96 to 0.97. "here are
exceptions where the emisaivity is as low as 0.90 or leas.
B. CONDUCTION COEFFICIENT
If the organism is in physical contact with a surface at temperature,
Tg, such as ground, rock, or tree trunk then energy is exchanged by
conduction. If the underlying surface is cooler than the organism, energy
is conducted from the organism into the substrate and if warmer than
the organism the underlying substrate will deliver heat to the organism.
For many animals this term is often of considerable significance. For
plant leaves the only possible conduction is into or out of the stem and
is usually negligible. The amount of heat conducted per unit area is
proportional to the temperature difference T, - To and to the conductivity, k, of the material. Hence,
Qcond = &Ts - T I )
(5)
The conductivity is the coupling factor between substrate and organism
temperature$.
c. CONVECTION COEFFICIENT
For organisms in air or in water, energy is exchanged by convection
in which molecular d i h i o n of heat occurs in the adhering boundary
layer at the organism surface and then mms movement occurs in the
fluid beyond the boundary layer.
1. 8tiU Air
Masa movement will occur in the case of natural conveotion due to