$6 Trans. Acad. Sci. of St. Louis. 



botanical collections ; the shading showing approximately 

 where collections have been made, and the density of it in- 

 dicating the number and extent of collections. The botanical 

 centers of the country of course show up as spots of denser 

 shading. The map is made up from lists of specimens found 

 in our large herbaria of several large genera of wide distri- 

 bution, species of which it would seem probable would be 

 found in all parts of the United States. It will be seen that 

 several regions of the west still need exploration. There is 

 also a comparatively blank space along the eastern side of the 

 Mississippi Eiver. Portions of Arizona and Colorado have 

 been well worked, and others are almost unknown. It may 

 be that certain parts of the arid regions show blank on the 

 map because of comparative dearth of species, northwestern 

 Texas and part of Nevada for example. Most of the prairie 

 region has been well explored, due to the energetic work in 

 State botanical surveys. 



There is a region extending from South Central Missouri 

 through Arkansas and Indian Territory to northern Texas 

 which is not perfectly covered by any of our manuals, which 

 has recently furnished many new species and others will, 

 with more exploration, no doubt be found. These are not 

 mere transition forms between the Eastern and Texan or 

 Western floras, but distinct species peculiar to this limited area 

 which is somewhat characterized by the Ozark Mountains 

 which may have isolated and preserved these peculiar forms. 



The Middle Western States like Missouri and Arkansas 

 would no doubt furnish a greater harvest for the " species 

 makers ' ' of recent years if they could be worked over as 

 thoroughly as some of the Eastern States by persons of such 

 tastes. 



It is desirable as an aid to the study of geographical dis- 

 tribution, variation and the formation of species, that every 

 distinguishable form, especially when they may also be geo- 

 graphically differentiated, should be published. However, in 

 these studies, no effort has been made to discover new forms, 

 although some have come to light simply in the determination 

 of the plants in certain collections. 



A study of the slightly variant forms of some widely dis- 



