40 MINNESOTA STUDIES IN PLANT SCIENCE 



Clavate filaments do not occur in the section. The subulate type pres- 

 ent is usually flattened with age and incurved more or less sharply at the 

 top. 



The receptacle is typically bowl- or urn-shaped, but varies considerably 

 within certain groups, such as that represented by S. integrifolia. The 

 relative depth of the receptacle furnishes a basis for dividing the species 

 into two principal divisions. 



Variations in the inflorescence are also marked within certain limits, 

 not only as between immature and mature stages but as between individuals 

 of the same species, as in 6^. nidifica and S. pennsylvanica. The writer has 

 not been able to determine whether the latter type is a specific or merely 

 an individual variation. A well-defined corymbose inflorescence occurs in 

 6'. fragosa and S. napensis. Glomerate cymules are characteristic of 5". 

 nidifica and its allies. 



Seed characters appear to be quite constant within certain groups. Thus, 

 winged seeds are characteristic of S. Slerrae and related forms, and 

 tuberculate seeds of 5". pennsylvanica and its allies. Intermediate forms 

 seem to show varying types, but in most cases the material has been defi- 

 cient in mature specimens. Several types of seeds have been found in 

 specimens referred to 5". pennsylvanica. 



The principal categories have been founded on the relative depth of the 

 receptacle — one shallow, the other deep. The species of the first division 

 are separated into two categories on the basis of petal-form, the first com- 

 prising all the species which have typically lanceolate petals, namely S. 

 pennsylvanica and allies, the second comprising a half dozen species which 

 have orbiculate or ovate petals, namely S. Sierrae and S. californica and 

 their allies. Characters of the follicles, petals, and leaves, since they are 

 constant within the limits indicated, serve to separate the minor categories 

 of each group, respectively. Finally the specific distinctions are based on 

 certain vegetative and floral characters that are well marked. In the second 

 division some dififerences in the gland occur, showing two lines of develop- 

 ment, one in which the type has remained constant, the other in which it has 

 become considerably narrowed, at least as far as could be determined from 

 the material available. The latter group is limited to a single species. The 

 remaining species, only six in number, are grouped in two categories on the 

 basis of the colors of the flowers. Characters of the petals serve to separate 

 the species of the first category'. The species of the second category fall 

 into two equal groups on characters of the inflorescence, in which the 

 species are designated by characters of the inflorescence and leaves. An 

 attempt has been made to arrange the species according to their affinities, 

 and If the specimens be laid out in series according to the accompanying 

 analytical key the significance of the arrangement may be evident. 



