Abstract
The various theories of the ascent of sap are discussed and it is concluded that the tension hypothesis best meets the observed facts. Seasonal and diurnal variations in water and gas content and the changes in tension that are demonstrable are all in accordance with the demands of the tension hypothesis. The two greatest problems are probably the maintenance in conducting channels of continuous water columns under high tensions without entry of air, and the refilling with water of such channels as do become gas-filled during the summer (for the insulation of gas and water channels one from the other is apparently not perfectly maintained). These problems are not entirely settled, though the hypotheses of Munch and/or Lund may account for the refilling of vessels in deciduous trees during the non-leafy season.The observed differences in the behavior of maple, birch and poplar during the period of sap flow have received attention. These peculiarities cannot be accounted for by differences in the root systems. The earlier cessation of bleeding and the development of tensions in poplar are correlated with a higher rate of evaporation from the twigs of the former, and this evaporation probably is largely through lenticels.The problem of sinkage, in the light of this work, is briefly reviewed.
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Claims 4
Claim · model-written summary
The tension hypothesis best fits observed facts about sap ascent.
Verbatim
e0“The various theories of the ascent of sap are discussed and it is concluded that the tension hypothesis best meets the observed facts.”
t0“THE PHYSIOLOGY OF THE TREE”
Claim · model-written summary
Seasonal and diurnal changes in water, gas and tension accord with the tension hypothesis.
Verbatim
e0“Seasonal and diurnal variations in water and gas content and the changes in tension that are demonstrable are all in accordance with the demands of the tension hypothesis.”
t0“THE PHYSIOLOGY OF THE TREE”
Claim · model-written summary
Differences in sap-flow behavior among maple, birch and poplar cannot be explained by root-system differences.
Verbatim
e0“The observed differences in the behavior of maple, birch and poplar during the period of sap flow have received attention. These peculiarities cannot be accounted for by differences in the root systems.”
Claim · model-written summary
Earlier cessation of bleeding and tension development in poplar correlate with greater twig evaporation.
PopulusNot reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The earlier cessation of bleeding and the development of tensions in poplar are correlated with a higher rate of evaporation from the twigs of the former”