PROGRESS IN PLANT MORPHOLOGY 607 



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 descrip- 

 tive 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 major 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 major 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, coni- 

 fers, Gnetales, angiosperms — we now see at least two lines: the Cycadophyte 

 and the Coniferophyte, with the Gnetales and angiosperms as lines with at- 

 tachment to the ancestral system still uncertain (the Gnetales are probably iso- 

 lated 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 pterido- 

 sperms 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. 



