6o8 EAMES 



Another outstanding feature of advance in the morphology of the past 

 fifty years is the rise of anatomy to a position of prominence in the inter- 

 pretation 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 — except in discussions of 

 "inside" versus "outside" growers and the origin of the woody stem from the 

 herbaceous with illustrations from — of all plants — the woody vines, Aristolo- 

 chia and Clematis. Unfortunately, even today, the dissected stele (frequently 

 illustrated by Ranunculus) is often described as characteristic of herbs, al- 

 though such a stele is rare in herbs. A casual study in New York State 

 showed the dissected stele present in less than 5 per cent of herbs. Fifty years 

 ago the herbaceous habit was generally accepted as primitive; today no one 

 questions its advanced nature. 



In the last few decades, the importance of critical studies of internal struc- 

 ture, both descriptive and comparative, has been recognized. Contributions in 

 the field of anatomy have been many and have greatly affected classification 

 and opinions of natural relationships. Note the evidence shown by stelar 

 structure in the breakup of the old Pteridophyta ; the evidence shown by 

 histological structure of the xylem in the classification of the conifers and the 

 primitive dicotyledons ; and the evidence of reduction provided by the vascular 

 vestiges of lost organs. 



Since simple plants clearly gave rise to complex ones, the apparently simple 

 forms in any taxon have long been accepted as the more primitive members. 

 Note the Amentiferae in the angiosperms. And some will remember when 

 aquatic monocotyledons were considered the most primitive angiosperms be- 

 cause of their resemblance to Isoetes. (The monocotyledons were then believed 

 to be more primitive than the dicotyledons.) Now, we question simplicity: 

 is it primitive or the result of reduction? And we are using more than one 

 character as evidence of simplicity. We look at the plant as a whole, at all 

 structure, external and internal. Comparison with related taxa shows series 

 in modification, series that often can be read in both directions. Here, internal 

 structure, with vestiges of lost parts, is critically important. And we must al- 

 ways, in reading series, consider evidence from other fields as well as mor- 

 phology. 



The recognition that simplicity often represents reduced complexity has 

 made great changes in our interpretation of the morphology of organs and the 

 classification of major and minor taxa. The flowers of the Amentiferae are 

 not simple ; their unisexuality, small numbers of sporophylls, and apetaly rep- 

 resent reduction. Reduction is also represented in angiosperms as a whole 

 by such structures as the solitary stamen, the basal ovule, the solitary micro- 

 spore. The naked flower may be primitive or advanced. The answer to the 

 question of primitive or advanced status of simple structure lies often in 

 comparison with related taxa, sometimes in ontogeny, often in the presence of 



