as in typical S. magnicamporum, the intensity of fra- 
grance was less than in typical plants of this species. 
Specimens of this race are, however, still recognizable as 
S. magnicamporum by the aspect of the inflorescence, the 
position of the lateral sepals, floral fragrance, the fuga- 
cious nature of the leaves, and the tuberosity of the roots. 
These plants occupy low calcareous black-soil prairie. 
They may occur over but a restricted portion of the range 
of S. magnicamporum, and I have recognized them only 
in northern Illinois. Judging from the numbers of speci- 
mens and known stations, this taxon seems to be par- 
ticularly well represented in the Chicago area, although 
this observation may reflect irregularities in collecting 
activity. 
It isapparent that these plants are intermediate between 
S. cernua and S. magnicamporum. Thus, this race may 
have arisen as a hybrid between S. magnicamporum and 
the sand prairie S. cernua. Evidently a portion of the 
resulting offspring became established in the edaphically 
hybrid habitat of low black-soil prairie. The presence of 
this race outside the range of the sand prairie S. cernua 
in Illinois suggests that this hybrid taxon spread from 
its point of origin to its present range across northern 
Illinois. It would appear most likely that the initial hy- 
bridization occurred in the Chicago area, where the great- 
est concentration of populations are to be found and 
where the necessary juxtaposition of the parents and low 
black-soil prairie occurs. 
It is not clear if a single or several hybridizations were 
involved in the founding of these populations: indeed, 
it is possible that similar populations have arisen inde- 
pendently at other localities in the range of iS. magini- 
camporum. Nor is the influence of backcrossing known. 
Variation between the parents occurs, but it is not known 
if this reflects segregation from a single initial hybrid 
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