20 MINNESOTA STUDIES IN PLANT SCIENCE 



the spreading calyx segments, the "filiform" stamens, and the '"semisu- 

 perior" ovary as the distinctive characters of the genus. 



The uniformly bottle-shaped carpels and the peculiar swollen ring-like 

 gland are the most distinctive characters of this section. The gland lies 

 a short distance above the base of the carpels in those species in which the 

 receptacle is very shallow; where the receptacle is deeper the gland lies a 

 short distance above the base of the calyx. Among some western species 

 the carpels and the glands are so strikingly alike that it is difficult to dis- 

 tinguish between them. But in such cases the type of inflorescence and 

 the form of the filaments serve to throw the species into categories whereby 

 their individual characteristics are projected and their identification thus 

 facilitated. The most pronounced deviation from the type appears in 

 Saxifraga carolinmna where the carpels and their beaks are very slender 

 and elongated. A deviation from the typical form of the receptacle is 

 found in S. nivalis where this structure is adnate to the carpels for about 

 half their length. In general the differences in the depth of the receptacle 

 are sufficiently pronounced to separate the species into two distinct natural 

 groups, one possessing a shallow, the other a deep, receptacle. The species 

 of the first category can be further separated on the characters of the 

 inflorescence into two nearly equal groups, one with a cymose, the other 

 with a paniculate, inflorescence. On comparison the species within each 

 group will appear to be quite closely related, so much so that on foliar 

 characteristics alone a number of them might easily be confused, as for 

 instance S. aequidentata, S. Marshalli, and S. Allenii, or S. caroUniana, S. 

 idahoensis, and S. microcarpa. 



The smaller categories are based on the characters of the filaments, 

 scapes, follicles, and petioles. Specific distinctions rest on the characters 

 of the leaves, sepals, scape, and follicles, where these are of sufficient con- 

 stancy and distinctiveness. 



Turning to the category in which the receptacle is deeper and also 

 broader, the division is made on the basis of the characters of the filaments 

 — one with subulate, the other with clavate, filaments. The species of the 

 first category here also show close affinity ; for example : S. virginiensis and 

 S. nivalis, which have been frequently confused. The two remaining 

 species, which comprise the clavate division, are readily distinguished by 

 the differences in size of the scapes and by the characters of the leaves. 



Geographically the species are confined largely to the United States. 

 Saxifraga nivalis, S. virginiensis, S. tennesseensis, S. Careyana, and 5". caro- 

 liniuna are species of the eastern United States. The two first named are 

 not clearly delimited as to their ranges. S. nivalis is circumpolar, being a 

 plant particularly of the Arctic regions. It is doubtful whether this species 

 actually occurs in the United States. No American specimens of it have 



