PROGRESS IN PLANT MORPHOLOGY 609 



vestigial vascular supply. For example, comparison with related taxa shows 

 the simple leaf of some legumes to be a surviving leaflet of a compound leaf, 

 as in Cercis and Crotalaria; that of other legumes, the result of the fusion 

 of two leaflets, as in Bauhinia and related genera. Vascular stubs in the 

 receptacle of the flowers of some Scrophulariaceae support the taxonomist's 

 interpretation made from comparison with other scrophulariaceous genera, 

 that stamen number has been reduced in the family from five to four, two, 

 and even one. 



Simplicity may be the result not only of reduction and loss but also of 

 fusion. External, and even internal, evidence of the fusion may be absent, for 

 the vascular system may be involved in the fusion. And ontogeny may be of 

 no help, because the fusion may have become fixed in phylogeny — may be 

 congenital. In 1910, in this country, the morphological significance of con- 

 genital fusion was not, or only rarely, recognized; today, morphologists, with 

 rare exceptions, recognize the importance of both ontogenetic and phylogenetic 

 fusion. 



A combination of fusion and reduction has brought about such morphologi- 

 cal complexities as the orchid flower — first correctly interpreted by Darwin, 

 with the aid of anatomy, nearly one hundred years ago. Today, though we 

 recognize the nature of the orchid column as the result of congenital adnation 

 and reduction, there is often refusal to accept the downward continuation of 

 this modification into the ovary. 



Parallel and convergent evolution were rarely mentioned at the beginning 

 of the century. Today, we recognize that parallel and convergent development 

 of morphological similarity of structure occur frequently. These similarities 

 may occur in any part of the plant; for example, a single leaflet surviving 

 from a compound leaf; one stamen representing an entire flower; the inferior 

 ovary; the basal ovule; the vessel. We recognize that parallel and convergent 

 evolution must be taken into account in interpreting all basic form and 

 natural relationships. 



Beginning as early as thirty years ago, morphologists urged that conclusions 

 as to natural relationships should be based on evidence from as many fields 

 as possible. Let me repeat: morphology and taxonomy alone are not in them- 

 selves sufficient for phylogenetic interpretation. Moreover, within the field 

 of morphology itself, evidence must come from internal as well as external 

 form, from skeletal form and structure, both gross and detailed — from stele, 

 xylem, phloem, and vestigial tissues. 



The acceptance of characters of diverse origin in the determination of 

 relationship has been steady though slow. A recent example, based on evi- 

 dence from vascular anatomy, cytology, and ontogeny, is the removal of 

 Paeonia from the Ranunculaceae and the establishment of the family 

 Paeoniaceae, in the Dilleniales, far from the Ranales. The Ranunculaceae 

 have commonly been called a natural family, but the removal of Paeonia 



