NUPHAR INTERMEDIA IN BRITAIN 



15 



coalesce and present a continuous ring of stigmatic surface on the disc. The rays them- 

 selves may be smooth or more or less furrowed, and their prominence above the surface 

 of the stigmatic disc is likewise variable. The central depression of the disc may be 

 shallow or deep, and with or without an umbo. The margin of the disc is characteristically 

 entire, a key " qualitative " feature distinguishing N. lutea and N. pumila; occasionally, 

 however, it is somewhat sinuous in N. lutea, as is found, for example, in some plants in 

 the population in Sutton Broad. . In Britain, at least, N. pumila appears to be not nearly 

 so variable in the character of the stigmatic disc ; the margin is uniformly deeply scalloped 

 and the stigmatic rays are linear. The axile process, however, may or may not be 

 developed. 



In N. intermedia the disc has a distinctly undulate margin (Fig. 6d) and so is inter- 

 mediate in this character between N. lutea and N. pumila. In the Chartners Lough 

 colony the stigmatic rays, although greater in number than in N. pumila, are similar in 



(c) (d) 



Fig. 8. Characteristic forms of peduncle anatomy in British Nuphar taxa. (a) N. lutea; (b) N. intermedia; 



(c) " introgressed " N. pumila; and (d) N. pumila, Sources of material as in Fig. 2. 



