12 Miller — Pond Lillics of Northeastern United States. 



nois, Indiana, and southern Michigan, that with floating leaves 

 in northern Ohio, eastern Michigan, and in Wisconsin, Iowa, 

 Minnesota, Montana and British Columbia. 



The most obvious structural peculiarities of the two plants 

 are found in the leaves. In the erect form the blade has some- 

 what pointed lobes and a widely open 

 sinus (well shown in the lower right 

 hand corner of the plate); petiole stout 

 and nearly terete (fig. 1 h). In the 

 floating form the lobes are rounded 

 and the sinus narrow or often com- 

 pletely closed by the overlapping 

 lobes. The petiole, relieved of all 

 strain of support, is conspicuously 

 flattened on the side corresponding to 

 the upper surface of the leaf (fig. 1 a). 

 This flattening robs the petioles of 

 ^_^^_^^__.^ , ^^ their strength so efi^ectually that they 



\ / ( ) are generally unable to hold the blades 



erect when, as sometimes happens, the 

 plants are exposed by low water. In 

 addition to its peculiar flattening the 

 petiole is marked by a median rib, the prolongation of the mid- 

 rib, and the margins are often, though not invariably, produced 

 as distinct wings.* 



The flowers and fruit though at first sight closely similar, 

 differ in several important details. In the northern plant the 

 inner surface of the sepals is almost invariably blotched with 

 purplish red near the base; while in the southern the correspond- 

 ing region is shaded with green. The fruit of the northern 

 plant is smaller, less ribbed and often strongly suffused with 

 red, while in the southern it is green throughout. Finally the 

 stigma rays are as a rule more numerous in the southern plant. 

 In 104 specimens of the latter collected at Four Mile Run, Va., 

 the number of rays varies from 10 to 23, but in 64 percent it 

 is between 14 and 17 (inclusive), with a well defined maximum 

 (20 percent) on 16. In 108 of the northern form from Chau- 



*It is of interest to note that the petiole of this plant is essentially th« 

 same as that of Nymphma lutea the common representative of the genus 

 in northern Europe. 



Fig. 1. Section of petiole 

 near middle: a Nymphaa 

 variegata, b JV. advena. 



