It seems impossible to have tensive channels in the presence of free air bubbles, which can occur when trees in cold climates freeze and then thaw. There is insufficient evidence for the existence of continuous water columns (that is, water columns under tension are not stable and they cavitate, or form cavities, hollows, or bubbles).ģ. The tensile strength of water is inadequate under the great tensions necessary to pull water to the top of plants, especially tall plants.Ģ. Objections to the theory include three major points (Kramer, 1983, p. The main difficulty is that it postulates a system of potentially great instability and vulnerability, although it is clear that the water-conducting system in plants must be both stable and invulnerable. Reprinted with permission of Brooks/Cole, a division of Thomson Learning: Fax 800 730-2215.) Wadsworth Publishing Company, Inc: Belmont, California. (From Salisbury, F.B., and Ross, C.W., Plant Physiology, 2nd ed., p. 19.2 The cohesion theory of the ascent of sap summarized. Even though most plant physiologists feel that the cohesion theory is probably the correct explanation for the rise of water in plants, the theory hasįIG.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |