228 JOURNAL OF THE ARNOLD ABORETUM [vol. ii 



The fact that the typically northeastern woody plants, associated 

 with many herbaceous species, in the Ozark region are usually confined 

 to the protecting bases of bluffs or steep hillsides having a northern or 

 eastern exposure, while those more characteristic of the arid southwest 



4 



are found in open rocky barrens or along the ledges and faces of cliffs 

 exposed to the hot southern or western sunshine, is not at all strange and 

 may easily be ex])laincd on ecological grounds; but it is at least suggest- 

 ive of how renmants of shifting floras may persist for a long time in pecul- 

 iarly favorable spots of a diverse region after the retreat of the main plant 

 formations to which they belong; and when many species grouped to- 

 getlier in well marked colonies are found isolated in such situations we 

 can scarcely escape the conclusion that they originated in some such way; 

 and we may well look to them for evidence of tlie directions such lines of 

 retreat or advance have taken. 



Besides the numerous localities throughout the Ozarks where colonies 

 of northern plants may be found growing in protected situations such as 



those referred to above there are occasionally found other colonies of aquite 

 different character with a somewhat boreal flora so peculiar for the 

 region as to deserve special recognition. One very interesting locality 

 of this class occurs along the bluffs and divides of Jack's Fork of Current 

 River, in Shannon County, Missouri. Here a number of plants rare in 

 this part of the country have been found and widely distributed amongst 

 botanists by Mr. B. F. Bush, with whom the writer visited the locality 

 in the autumn of 1920. Most of the peculiar species found here, as in 

 the southwestern barrens, are herbaceous, and consequently a detailed 

 description, will not be entered into at present, but amongst many in- 

 teresting species are such plants as Campanula roiundifolia L.?, Farnassia 

 grandijlora Raf., Traxdvetteria caroUniensis Vail, Plaiitago cordafa Lam. 

 and Galium boreale L. Two notable shrubs far from their general range 

 here are Berheris canadensis Mill, and Coruus alternifolia L. Nearly all 

 of the peculiar localized plants of this colony are growing in sandy soil, 

 resulting from the disintegration of Cambrian sandstone, whicli appears 

 at the surface here. Some of them are growing in open sunny situations 

 ui)on the high ridges, some on the slopes and face of the bluffs and others 

 in boggy ground along small streams. 



Anyone who has followed this brief sketch of the Ozark region and its 

 flora can scarcely have failed to perceive that the facts set forth clearly 

 inrlicate that there has been a gradual advance of the forests from the 

 south or southeast toward the northern portion and, moreover, that the 

 northward movement was one of coniparatively recent inception and that 

 it is still in active progress. And to one who has had an opportunity to 

 view the Ozark country and its flora throughout its length and breadth, 

 and who is also somewhat familiar with the floras of the surrounding 

 regions, there can be no doubt as to the direction of the forest invasion 

 and the source from whence it has ccmie. More involved but certainly 

 not less interesting are the questions of what were the geographic, 



