1903.] NATURAL SCIENCES OF PHILADELPHIA. 661 



specialists on the genus returned as belonging to twice that number 

 of species, due to the difference in their identifications. 



Variation in the Genus Viola. 



My observations on the genus Viola as represented in the neigh- 

 borhood of Philadelphia have covered a number of years, but during 

 the past three seasons the study has been carried on systematically 

 throughout the spring and summer. Typical colonies of the various 

 forms have been constantly under observation, and large series of speci- 

 mens have been preserved at definite periods which show as nearly as 

 possible the changes undergone by each species. These specimens 

 will be distributed in sets to several of the principal herbaria in the 

 East, where they may perhaps be of assistance to others who are 

 engaged in a study of this interesting genus. 



The species of the genus Viola are divisible at once into two groups — 

 the caulescent species, bearing both leaves and flowers upon a main 

 stem, and the acaulescent, in which petioles and scapes spring from 

 the root stalk. The species of the former group are much more easily 

 defined, and show but little of the tendency to racial variation that is 

 characteristic of the acaulescent group. We find three types of color 

 in the flowers of the genus — blue, yellow and white— and all are repre- 

 sented in each of the above groups. In one caulescent species V. 

 rafinesquii the flowers are somewhat parti-colored, as in the case of the 

 pansies of cultivation, of which this is our native representative, 

 forming a section well distinguished from the other species by addi- 

 tional characters. Among the caulescent species we also have one 

 parti-colored race, V. pcdata, which likewise is clearly separated from 

 the others by structural peculiarities. 



It is the blue-flowered acaulescent species that present b}^ far the 

 greatest racial and individual variation, and it is to them that I have 

 given particular attention, and upon which the following statements are 

 based, though all the species are considered in the review of our local 

 violets which concludes the paper. 



Leaf-form is decidedly the most striking character in violets, and 

 one in which variation is to be seen to perfection. There is, first of 

 all, variation due to age, the early leaves being usually different from 

 those produced later in the season. The general shape of the early 

 leaves is, moreover, very similar in a number of species which later on 

 bear but little resemblance to one another — a fact which renders it 

 exceedingly difficult to identify some of the descriptions of older 

 writers based solely upon early flowering plants. In forms in which 



