418 MORPHOLOGY OF THE ANGIOSPERMS 



appendages. Evidence from the vascular skeleton is essential to the 

 morphological interpretation of these flowers. (The growth of the re- 

 ceptacle about the carpels in Nehimbo is not evidence that, in other 

 genera, the receptacle has similarly surrounded the bases of all ap- 

 pendages. ) 



Comparison is frequently made between the gynoecium of Nelumbo 

 and that of Eupomatia, a primitive woody ranalian genus; both genera 

 are described as having carpels sunken in the gynoecium. This com- 

 parison is invalid, because the carpels of Eupomatia are connate and 

 intimately fused, basally (Fig. 72A). 



The Nymphaeaceae and Cabombaceae provide examples of a rare 

 type of placentation (Fig. 85) — few or solitary ovules, representing 

 reduction directly from typical laminar placentation with many ovules. 

 Solitary and paired ovules in most families are survivors of submarginal 

 placentation, a stage intermediate between laminar and solitary ar- 

 rangement. In laminar placentation, ovule traces are derived from the 

 meshwork of small veins and also duectly from the midvein and major 

 lateral veins; in submarginal placentation, the ovule traces are derived 

 directly from the ventral bundles only. (The reduced placentation in 

 these families is described in Chap. 6.) 



The relationships of the Nymphaeaceae have long been in question. 

 The family has been considered, in some characters, transitional to the 

 monocotyledons, especially in the possession of scattered vascular bun- 

 dles in the stem and of laminar placentation. The water lilies have even 

 been called monocotyledons; the presence in NeJumbo of a so-called 

 single cotyledon has been used as partial evidence for this classifica- 

 tion. But this cotyledon has been shown to consist of two cotyledons, 

 connate at the base. In flower characters, general resemblance has been 

 seen between the Nymphaeaceae and the Helobiales, and the sugges- 

 tion made that the water lilies should be placed either in this mono- 

 cotyledonous order or considered transitional to the monocotyledons. 



The Nymphaeaceae and Cabombaceae form an isolated, heteroge- 

 neous ranalian assemblage, showing progressive stages in specialization 

 in both external and internal structure. 



Lauraceae 



The Lauraceae are relatively more advanced than most of the ranalian 

 famflies but belong with these families in a comparative and phylo- 

 genetic discussion. The family consists largely of tropical and sub- 

 tropical trees and shrubs. In both external and internal characters, it is 

 intermediate between most of the Ranales and more advanced orders. 



The flowers show stages in transition from bisexual to unisexual. The 

 simple, inconspicuous perianth of six members has been interpreted as 



