Anatomy of the Primary Vascular System in Dicotyledonous Plants

Abstract

A STRIKING feature of botany as the science XJL exists at prej ift is the lack of any coherent body of comp£"n?ive morphological doctrine dealing with bd aimKspernis. There are no books on the ncmeftjp plants in any way comparable with Bower's wW the ferns or Chamberlain's on gymnosperms. Asia result, the treatment of angiosperms in university courses on botany is usually confined to separate and unrelated series of lectures on systematics and on plant anatomy. In seeking a remedy for this remarkable situation one cannot but be impressed by the almost complete neglect of the gross anatomy of the primary vascular system, or what the older anatomists called "the course of the vascular bundles in the stem". Analogy with the study of other groups suggests that this department of anatomy may be expected to yield data of phylogenetic significance. The pioneer paper published by Nageli1 in 1858 is still our principal source of information on this topic, the few memoirs which have appeared since that date being for the most part descriptions of the development of single species or accounts of the more obviously aberrant groups such as Piperacese. There have also been some publications dealing with the number of traces to a leaf in various families (for example, Sinnott2). The neglect of the subject may be attributed almost entirely to the fact that Nageli and nearly all subsequent writers have paid altogether too much attention to the supposed basipetal development of the leaf traces, and have described vascular systems in terms of traces running down the stem and joining on to the traces of older leaves. Descriptions framed in this way make very tedious reading, and are so ill-adapted to the comparison of related vascular systems as to be' almost unintelligible without the aid of diagrams. Furthermore, such accounts tend to emphasize relatively trivial features, especially the numbers of internodes which the various bundles traverse, at the expense of others which are really far more important.