MINNESOTA BOTANICAL STUDIES. 



sandstone. There are rocks near the park containing lime, but 

 they did not seem to support any lichens of special interest. 



The collecting was all done on the Minnesota side of the 

 river for the reason that the erosion of the valley has been such 

 as to leave better exposures of rock here than on the Wisconsin 

 side. I had collected from excellent exposures of igneous rocks 

 in New England and have since visited similar ones in various 

 parts of northern Minnesota ; but I have never seen any other 

 equally limited area of rock exposure that aroused so much in- 

 terest, because of richness of lichen flora and evidence of mi- 

 grations and struggle, as did this little area, set aside for an 

 interstate park. During the trip of 1897 I noticed that the con- 

 stant tramp of feet had begun to kill out the lichens in many 

 places so that the impression of richness is beginning to fade, 

 and the botanist must soon seek some place near by, if such ex- 

 ists, where he may study this rich flora in its natural beauty. 



Professor E. E. Edwards, of Lancaster, Wisconsin, writes 

 thus of the lichens found in the park: "The rocks of the 

 Dalles owe their beauty and variegated tints not alone to the 

 metal oxides, or to the feldspar or hornblende chiefly composing 

 them, but to the growth of minute lichens upon their surfaces, 

 and these vary in color according to the dryness or moisture of 

 the atmosphere. We have, therefore, in these, through sunshine 

 and shadow and the varying seasons, an endless and almost 

 kaleidoscopic play of colors that makes them alike the delight 

 and despair of the artist." The little area, being one of great 

 natural beauty and set apart for an interstate park, will always 

 attract thousands of visitors annually and I hope to present in 

 this paper thoughts which will enable the botanist who has a 

 fair knowledge of lichen species and their distribution to see in 

 this wonderful lichen population something of far greater inter- 

 est than mere beauty. 



Some comparisons between the locality now under considera- 

 tion and others will best show its richness in rock lichens. The 

 area examined covers only a few acres of surface and gave 66 

 lichens growing on rocks as a result of two days' collecting. 

 The whole region about Minneapolis when more thoroughly 

 worked only furnished 30 saxicolous lichens, and the whole of 

 Fayette county, Iowa, only 50. The latter region is surely 

 better than the average for rock lichens, and I have studied it 

 for six years. Probably however, the fact that I have not looked 



