MILLER AND STANDLEY—-NORTH AMERICAN NYMPHAEA. TT 
-of fertility than other members of the genus, so much so that ripe fruit with well-devel- 
oped seeds is not easily obtained. In geographic range it appears to be a boreal form, 
occurring therefore in the same region as NV. microphylla, and in that part of the range of 
N. americana which extends north of the Transition Zone and overlaps that of the 
smaller plant. All of these facts might readily be construed as indicating a hybrid 
origin. On the other hand the characters of Nymphaea rubrodisca are quite as con- 
stant as in other American species, and no specimens are yet known which show any 
tendency to reversion toward either of the supposed parents. The plant is by no 
meansinvariably found locally associated with both N. americana and N. microphylla, as 
s 
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Fig. 7.—Map showing distribution of (a) Nymphaea ovata; (b) N. rubrodisca; (c) N. ludoviciana; (d) N. 
ulvacea; (e) N. bombycina; (f) N. sagittifolia. 
either or both of these may be absent from the particular stream or pond in which it 
grows;' while in general distribution it extends decidedly beyond the western limit of 
the range of N. microphylla as now known. Finally, it is not unusual among plants for 
certain members of a genus to produce fruit less abundantly than others, particularly 
in groups where asexual reproduction and dispersal can readily occur. The hypothe- 
sis of hybrid origin seems, therefore, to present the greater number of difficulties, and 
until more facts can be brought to its support we prefer not to accept it. 
1Tt was found thus alone by Peck at the type locality of hybrida, 
