Carlquist Sherwin, Schneider Edward L
Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, California 93105 USA.
Am J Bot. 2002 Feb;89(2):185-95. doi: 10.3732/ajb.89.2.185.
Current definitions of tracheids and vessel elements are overly simple. These definitions are based on light microscope studies and have not incorporated information gained with scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Current definitions are based primarily on angiosperms, especially eudicots, and were devised before many basal angiosperms were carefully studied. When all sources of information are taken into account, one can recognize changes in six characters in the evolution of tracheids into vessel elements in angiosperms (or vice versa) as well as in other groups of vascular plants. There is an appreciable number of taxa in which all criteria for vessel origin are not met, and thus incipient vessels are present. At the very least, vessel presence or absence should not be treated as a single binary character state change in construction of cladistic matrices. Increase in conductive area of an end wall by means of lysis of progressively greater areas of pit membrane and increase in pit area on the end wall (as compared to pit area on equivalent portions of lateral walls) are considered the most important usable criteria for recognizing intermediacy between tracheids and vessel elements. Primitive character states in vessel elements are briefly discussed to differentiate them from changes in character states that can be regarded as intermediate between tracheids and vessel elements.
当前对管胞和导管分子的定义过于简单。这些定义基于光学显微镜研究，并未纳入通过扫描电子显微镜（SEM）或透射电子显微镜（TEM）获得的信息。当前的定义主要基于被子植物，尤其是真双子叶植物，并且是在许多基部被子植物被仔细研究之前制定的。当考虑所有信息来源时，人们可以识别出被子植物（或反之亦然）以及其他维管植物类群中管胞向导管分子演化过程中六个特征的变化。有相当数量的分类群不符合导管起源的所有标准，因此存在初始导管。至少，在构建分支矩阵时，导管的有无不应被视为单一的二元性状状态变化。通过逐渐更大面积的纹孔膜溶解来增加端壁的传导面积，以及端壁上纹孔面积的增加（与侧壁等效部分上的纹孔面积相比）被认为是识别管胞和导管分子之间中间状态的最重要可用标准。简要讨论了导管分子中的原始性状状态，以将它们与可被视为管胞和导管分子之间中间状态的性状状态变化区分开来。
