Fink: ROCK LICHENS OF TAYLORS FALLS. 9 



climate and stated that, were it not for peculiarly unfavorable 

 conditions as to rock-formations, this explanation would require 

 a larger per cent, of the total number of lichens found there to 

 occur on the rocks because of greater amount of moisture near 

 the ground. The annual precipitation at Osceola Mills for the 

 last six years has been 31.271 inches, while at St. Paul it has 

 been 28.997 inches. The former place being only seven miles 

 from Taylors Falls, the figures may be taken to show that 

 the precipitation in the locality now considered is about 2.274 

 inches more per annum than that at Minneapolis. Hence we 

 have at Taylors Falls essentially the same conditions as to mois- 

 ture of atmosphere as at Minneapolis. However at the former 

 place we have the extensive rock-formations necessary for the 

 establishment of the plants, and we find further that the igneous 

 rocks are favorably situated for lichen development in that they 

 lie along a river course formerly better shaded than now and 

 where moisture has been abundant in spite of comparative dry- 

 ness of atmosphere. Also this flora was doubtless largely es- 

 tablished when the climate was not so dry as now and is persist- 

 ing against conditions less favorable than formerly existed. 

 Moreover the 8 persisting northern species add to the number 

 strictly characteristic of present climate and give the locality a 

 further advantage over Minneapolis and vicinity. Doubtless 

 study of the whole lichen-flora about Taylors Falls would show 

 that between 30 and 50 per cent, of the lichens grow on rocks 

 as compared with 12 per cent, at Minneapolis. The slight ad- 

 vantage in annual precipitation of moisture for the former lo- 

 cality, of course, adds slightly to the relative richness in rock 

 lichens, but this is insignificant as a cause when compared with 

 the elements considered above. 



Another objection of doubtful value to the first proposition 

 suggested to account for the invasion of the northern rock-floral 

 elements is that, though there is a continuous line of conifers 

 from Lake Superior to Taylors Falls, the northern tree-inhab- 

 iting lichens are wholly absent at Taylors Falls, or so scarce 

 as to escape notice. The coniferous trees are not so conspicu- 

 ous a part of the flora at Taylors Falls as in Pine county, fifty 

 miles north. No doubt at least a part of the tree lichens char- 

 acteristic of more northern regions, and now almost certainly to 

 be found in Pine county, have extended down to this location 

 in post-glacial times, as the conifers are abundant from Lake 



