426 MORPHOLOGY OF THE ANGIOSPERMS 



the Dilleniales have numerous stamens (reduced in HibheHia) and 

 those of the Ranales only three, or perhaps five, without evidence that 

 these numbers represent reduction. Fasciculate stamens appear to have 

 arisen independently in the two orders. 



Carpels. The carpels of the Ranales show primitive laminar structure 

 comparable with that of the stamen and with similar stages in elabora- 

 tion of form related to function — in the stamen, anther, and filament; in 

 the carpel, stigma, style, and ovary. The most primitive carpel, well 

 shown in Drimijs (Fig. 72C) and Degeneria (Fig. 72F), is folded, but 

 unsealed; pollen-receiving areas are on marginal bands of the external 

 and internal surfaces throughout the length of the lamina, and the pollen 

 tubes enter between the marginal lips of the lamina. The two 

 marginal strips projecting at the tip of the folded carpel show the origin 

 of the two-lobed ( unicarpellate ) stigma of some liigher orders. (The 

 bilobed stigma is not the result of a basic dichotomy in the sporophyll.) 

 The frequent presence of a stipe in the Ranales supports the view that 

 the ancient carpel was stipitate, resembling a petiolate leaf. 



The retention of sporophylls so leaflike and undifferentiated as those 

 of Degeneria, Drimi/s, Magnolia, Nijmphaea, Lactoris is remarkable in 

 an order with many highly advanced characters. 



The families of the Ranales show different methods of derivation of 

 the isolated terminal stigma from the primitive stigmatic ridge, which, 

 in Degeneria and many species of Drimt/s, extends the full length of 

 the carpel. Progressive acropetal shortening and distortion of carpel 

 form brought the stigmatic area to a pseudoterminal position in Drimijs; 

 sterilization and constriction of the distal part of the carpel formed a 

 terminal stigma in Himantandra; connation of many carpels en masse 

 in Eiipomafia restricted the stigmatic area to the tips of the carpels. 

 Other taxa show the style as an elongation of the distal part of the 

 carpel. 



The restriction of ovules to areas directly below the shortened stig- 

 matic crest is perhaps evidence that, in early angiosperms, pollen tubes 

 were short — as in Degeneria and the Winteraceae, where the pollen 

 grains germinate close to the ovules — and that the long tube is corre- 

 lated with the presence of a style. 



The stipe — perhaps homologous with the petiole — characteristic of 

 the primitive carpel in the Ranales, is present in other primitive orders, 

 especially the Resales; it is greatly reduced or lost in some ranalian 

 families. 



Placentation. In placentation, the history of evolutionary modification 

 is one of progressive reduction in ovule number and in fertile wall area. 

 Accompanying these changes has been modification of the relation of 

 ovule traces to the vascular system of the carpel lamina. The ranalian 



