Certain Ecological and Phylogenetic Aspects of the Pattern of Water Conduction in Conifers

Abstract

THE DEVELOPMENT of a water-conducting system in plants is one of the elements in evolution that reflects the plant's conquest of a new environment. Naturally, the progress of this development is most pronounced in those plants whose water must ascend a long distance from the roots to the transpiration surface and against the force of gravity, i.e., in trees. The phenomenon of water transport consists of a static component, the conducting elements, and a dynamic component, the forces effecting the ascent. The water transport in conifers is effected by tracheids, which form the water-conducting elements, or tracheidal conduits or channels. Besides this axial transport of water in the tracheids, some limited radial and tangential translo-cation also takes place, but it will not be considered here. The present discussion is concerned with the pattern of axial water transport and the arrangement of the conducting elements in the stems of conifers. A simple method to ascertain the pattern of water transport has been described in detail (Vit•, 1959). In brief, acid fuchsin, in a 0.3 to 1 percent aqueous or alcoholic solution, was injected into the trunk through a hole bored into the base of the tree or by means of an injection knife. After a few days, the distribution of the dye within the tree was studied by sectioning the trunk transversely at regular intervals above the point of injection. A clear picture of the existing pattern of water conduction is obtained from the active crown, whereas certain alterations can take place below the active crown that may distort the pattern (Vit• and Rudinsky, 1959). Therefore, young trees (10 to 20 years old) as well as middle-aged ones (40 to 80 years) were chosen. In contrast to the methods used and the results obtained by Greenidge (1955 and 1958) in his studies on the water ascent in broadleaf trees, it was found that the dye followed the grain in every instance; the stained pattern obtained was identical to the arrangement of the tracheidal conduits within a stem (Vit• 1958 and 1959). Anatomlcal differences in the xylem structure cause the different patterns of water conduction, although individual specimens within a species may show considerable variation. The study of various conifers led to the detection of five water-conducting systems (Vit• and Ru-dinsky, 1959) which are summarized as follows: 1. Spiral ascent, turning right: On the transverse section, the stained pattern forms a spiral band that runs from the out-ermost growth ring clockwise toward the center of the stem.