P. F. Scholander

Sap Pressure in Vascular Plants: Negative hydrostatic pressure can be measured in plants

A method is described which permits measurement of sap pressure in the xylem of vascular plants. As long predicted, sap pressures during transpiration are normally negative, ranging from -4 or -5 atmospheres in a damp forest to -80 atmospheres in the desert. Mangroves and other halophytes maintain at all times a sap pressure of -35 to -60 atmospheres. Mistletoes have greater suction than their hosts, usually by 10 to 20 atmospheres. Diurnal cycles of 10 to 20 atmospheres are common. In tall conifers there is a hydrostatic pressure gradient that closely corresponds to the height and seems surprisingly little influenced by the intensity of transpiration. Sap extruded from the xylem by gas pressure on the leaves is practically pure water. At zero turgor this procedure gives a linear relation between the intracellular concentration and the tension of the xylem.

Heat regulation in some arctic and tropical mammals and birds.

A series of arctic and tropical mammals and birds at Point Barrow, Alaska (lat. 71° N.) and in Panama (lat. 9° N.) was subjected to various air temperatures in a respiration chamber where the heat production was determined by oxygen consumption or carbon dioxide production. The larger arctic mammals and birds showed no increase in metabolism at — 30° C. and from observations on sleeping animals it is probable that their zone of thermoneutrality extends to — 40° C. or — 50° C. The smaller arctic species show a high critical temperature and the tropical species even higher. Metabolic heat production increases rapidly with lowering of the temperature in a tropical mammal or bird, and slowly in an arctic animal. It can be shown theoretically that in a thermoregulated system with a fixed basal energy level and variable insulation the critical gradient is proportional to the maximal insulation and the basal energy level.In a large series of experiments including our tropical and arctic animals, and all animals ...

BODY INSULATION OF SOME ARCTIC AND TROPICAL MAMMALS AND BIRDS

Insulation measurements on raw skins from 16 arctic and 16 tropical mammals are given. There is, as would be expected, a good correlation between the thickness of the fur and the insulation. The smaller arctic mammals (weasels, lemmings) have much less insulation than the larger and overlap many of the tropical forms. From the size of a fox to the size of a moose there is no correlation between insulation and body size, they all have about the same insulation per surface area. When submerged in ice water, seal blubber retains about the same good insulation, as compared with measurements taken in 0° C. air. In the polar bear, heat transfer through the fur increases 25-50 times when submerged, because of complete wetting of the skin surface and absence of blubber. The beaver is slightly better off when submerged, as it retains an insulating layer of air in the fur next to the skin.

ADAPTATION TO COLD IN ARCTIC AND TROPICAL MAMMALS AND BIRDS IN RELATION TO BODY TEMPERATURE, INSULATION, AND BASAL METABOLIC RATE

Maintenance of constant body temperature in a homoiothermic animal depends upon a balance between heat production and heat dissipation, and there are consequently three possible main avenues for climatic adaptation, (1) by body-to-air gradient, (2) by heat dissipation, and (3) by metabolic rate. There is no evidence of adaptive low body temperature in arctic mammals and birds, or high body temperature in tropical mammals and birds. The body-to-air gradient can be adapted only by means of behavioral thermoregulation (nest building, avoidance of direct sunshine, etc.). With few exceptions our adult arctic and tropical mammals and birds have a basal metabolic rate that fits the standard mouse to elephant curve, i.e., the basal metabolic rate is determined by an exponential relation to size; evidently fundamental to most animals, warm-blooded or not. The basal metabolic rate is consequently not influenced by such factors as temperature gradient and insulation which largely determine the heat loss, and is henc...

Climatic Adaptation in Arctic and Tropical Poikilotherms

in response to white and monochromatic lights following differential adaptation of the eyes to various light stimuli. 3. The ability of Drosophila to discriminate among wave lengths is lost with a reduction of intensity to a level previously shown to involve a photoreceptive mechanism different from that shown to operate in bright light. 4. The color-differentiating capacity appears, therefore, to be associated with a high-illumination receptive mechanism (photopic) in a manner paralleling that in the vertebrate eye. 5. The dim-light receptive mechanism (scotopic) lacks color-differentiating capacity. 6. The results indicate that there are

SECRETION OF GASES AGAINST HIGH PRESSURES IN THE SWIMBLADDER OF DEEP SEA FISHES I. OXYGEN DISSOCIATION IN BLOOD

1. Oxygen dissociation curves at a P02 running from 0.2 to 140 atmospheres have been obtained from eight species of deep sea fishes, at a pH varying from 8.0 to 5.7 and at a CO2 tension from 0.03 to 10-20% of one atmosphere.2. The Root effect in acidified blood could be demonstrated in some of these species even up to 140 atmospheres, inasmuch as part of the hemoglobin remained unsaturated. In other species full arterial saturation occurred, however, at pH 6 or lower, at oxygen tensions much lower than those existing in the swimbladder. Hence the Root effect is not the mechanism for the oxygen secretion in deep sea fishes. If oxygen is derived from oxyhemoglobin it must be unloaded by some mechanism as yet unknown.

SECRETION OF GASES AGAINST HIGH PRESSURES IN THE SWIMBLADDER OF DEEP SEA FISHES II. THE RETE MIRABILE

1. The structure and dimensions are given for the rete mirabile. It is interpreted as a counter current diffusion exchange mechanism between the afferent and efferent rete.2. This diffusion exchange has been quantitatively evaluated for O2, CO2, and N2. The arrangement makes possible the maintenance of a steep tension gradient within the rete, so that the oxygen loss from the leaving blood can be extremely low.3. Quantitative evaluation of the efficiency of the rete diffusion makes it clear that the limiting equilibrium pressure in the swimbladder could be extremely high, and that the limiting factor lies mainly in the dissociation pressure of the chemical or physical reaction which ultimately splits off the oxygen.4. The nature of the responsible compound and reaction is unknown. The anatomical arrangement of the glandular structure and the rete is suggestive of a cellular secretion of oxygen rather than of a mechanism that splits off oxygen in the blood.5. Data on the deposition of nitrogen against high...

COMPOSITION OF THE SWIMBLADDER GAS IN DEEP SEA FISHES

1. The composition of the swimbladder gas has been determined in 26 species (260 specimens) of marine deep-sea fishes taken at known depths between 200 and 950 meters.2. The partial pressure of nitrogen in the bladder steadily increases with depth until it reaches some 5-15 atmospheres at a depth of 900 meters, revealing that not only oxygen but also nitrogen is transported into the swimbladder against a considerable gradient. This corroborates the findings of Hufner (1892) that the whitefish (Coregonus) is able to secrete pure nitrogen against a hydrostatic pressure of 6-8 atmospheres.3. The data, together with previous observations from shallower depths, show that the nitrogen tension at all depths may be expressed by (1) a diffusion term of 0.8 atmosphere, plus (2) a secretion term which, although different for different species of fish, is in each species a constant percentage of the total secreted gas pressure. Among our fish the secretion term ranges from about 2% to 15% nitrogen. In the whitefish i...

Supercooling and ice propagation in blood from arctic fishes

Abstract Studies of melting points and rates of freezing of plasma from winter fishes in the Bering Sea show that they survive in a supercooled state. The striking hysteresis in their melt-freeze equilibrium is related to the colloid fraction of the plasma. The lack of effect on the melting point and the modified crystal growth (monocline) when the supercooling breaks down suggests that the freeze protection involves shielding of the water-ice interface.

Volumetric Plastic Micro Respirometer

A simple plastic micro respirometer is described based on a direct reading volumetric principle. The respiration chamber with CO2 absorber is balanced against a compensating chamber through a manometer drilled in Lucite. As oxygen is used it is replaced from a syringe so as to maintain balance with the compensating chamber. The oxygen consumed is read directly on the syringe. Two sizes have been made covering a range of oxygen consumption from 10 mm3 to 10 cc per hour.