SOME ASPECTS OF PROGRESS IN PLANT MORPHOLOGY DURING THE PAST FIFTY YEARS

FIFTY YEARS AGO as an undergraduate, I was learning about vascular cryptogams and seed plants and how the herbaceous stem Lecomes the woody stem. In secondary schools, pupils were studying about "exogens" and "endogens" and how to identify the wild flowers. Morphology in this country-as illustrated by the general textbooks of that dayconsisted almost entirely of the descriptions of plants and their life histories. Classification was based largely on single characters. Internal structure was seldom mentioned. Comparative morphology was only beginning to receive attention. Progress in the morphological field has been remarkable, even extraordinary, as we look back and try to outline it. Advance has followed many lines: first, the acquisition of much factual material, necessary as a foundation for comparative interpretations, and for the testing of earlier theories and the proposal of new ones; secondly, the development of emphasis on the comparative viewpoint -the use of the more abundant descriptive material for the determination of evolutionary progress in form, and thus for the establishment of probable natural relationships. The development of comparative study produced new bases for interpretation: the recognition that sound morphology must deal with the entire plant body, with vegetative as well as reproductive parts, with internal as well as external structure; the recognition that simplicity may represent reduction from complexity as well as primitiveness; that parallel and convergent evolution have played an important part in evolutionary modification; that evidence of these changes is as often hidden as obvious and must be obtained from as many fields of research as possible-not from morphology alone, but from taxonomy, cytology, genetics, geography, paleobotany, serology, and other fields. In the light of the broader viewpoint of today, the morphology of the beginning of the century seems almost archaic. Because of the limited time available, I am restricting this discussion to a narrow field, to what is called "classical morphology" and to vascular plants, especially the angiosperms. Looking broadly, first, over this field: the study of the entire plant body rose rapidly to prominence; it soon became unnecessary to announce a course in morphology as "comparative"-as was customary in the earlier decades of the century. All morphological study was soon accepted as both descriptive and comparative (comparative in the sense of evolutionary modification). Comparative study of the plant as a whole 'brought great changes in the classification of the maj or taxa of vascular plants and the drastic modification of the pretty evolutionary tree, so long dear to the teacher's heart. The change was far-reaching because it involved the discard of the seed as the basis for delimitation of maj or taxa and the breakup of the seed plants as the taxon representing the highest attainment in the plant world. The seed had come to be accepted as the ultimate step in reproductive methods, and the fact that the seed might have developed independently more than once did not enter the picture. Study of the entire plant body has shown that other characters are at least as important as the seed. The union of the seed plants with the ferns in the new taxon, Pteropsida, seemed to many botanists an unholy one, so deep-seated had the value of the seed as a distinguishing character become. Almost as difficult to accept was the separation of the ferns from the horsetails and club mosses, so long their close "allies." The separation, a little later, of the horsetails from the club mosses, as unrelated taxa, came more easily. The Phanerogams-the seed plants of the early nineteen hundreds-have similarly seen extensive changes in classification, and the new treatment, a dissection into isolated groups, receives continuing support from evidence in many fields. In place of the direct-line, tree-trunk relationship-cycads, conifers, Gnetales, angiosperms we now see at least two lines: the Cycadophyte and the Coniferophyte, with the Gnetales and angiosperms as lines with attachment to the ancestral system still uncertain (the Gnetales are probably isolated end-products of more than one ancestral line). As we understand the Gymnosperms today, they are a highly unnatural taxon, consisting of at least two clearly distinct lines, with the ancient pteridosperms a possible third, ancestral to some or to all of the others. The term Gymnospermae is no longer useful in a natural classification. Protests arise now and then that morphology is becoming phylogeny: that it is no longer a "pure" science. But the study of morphology is, above all, the study of evolutionary modification of form. And theories of the basis of change in form can be interpreted only in the light of its relationship to natural classification; morphology must go hand in hand with other fields in the establishment of phylogenetic relationships. Another outstanding feature of advance in the mnorphology of the past 50 years is the rise of anatomy to a position of prominence in the interpretation of form and in the support of theories of phylogenetic relations. In descriptive morphology, anatomy played only a minor part in the elementary textbooks of the early decades of this century-ex-