Fink: LICHENS OF THE NORTHERN BOUNDARY. 173 



found for the first time to give detailed attention to the lichen 

 communities of wet rocks and to the poplar tree formations 

 about Lake of the Woods. The Umbilicaria formations also 

 were studied ecologically for the first time, and the Cladonias 

 of humus over rocks as well. Finally, a brief mention of the 

 unusually large number of lichens found living parasitically on 

 other lichens is in order. 



In passing to the consideration of formations, it may be said 

 that, as in the previous studies of this series, in covering so 

 large a region in limited time and making extensive collections 

 and taking notes on ecologic distribution at the same time, it 

 was not found possible to give attention to other than the more 

 general ecological considerations. Some general statement 

 may be made of various adaptations noted and not previously 

 reported, and some of them must be taken as merely sug- 

 gestive and as yet little more than mere guesses thrown out 

 with the hope that others may be inclined to study some of them 

 more in detail. First of all, it is certain that, in many of the 

 fruticose lichens as the Ramalinas, some Cetrarias, Evernias, 

 UsneaS) Stereocaulons and Cladonias ^ there is in dry weather a 

 drawing together of branches as if to lessen exposure to wind 

 and lessen transpiration of moisture. The same seems true of 

 the crisping and bringing together of lobes in many of the foli- 

 ose species in dry weather or the dry portion of a day. This 

 may be seen in Peltigeras, some foliose Cctrarias and certain 

 Nephromas, Leptogiums, Collemas and Theloschistes. The 

 writer has made some preliminary studies on Peltigera and 

 Ramalina and is convinced that some species of the former 

 genus are as responsive to moisture relations as are certain seed- 

 plants as Oxalis and many legumes to light and temperature. 

 Also he believes that many lichens are quite responsive 

 to light and temperature conditions in passing from their 

 moist flexible state to the dry and fixed condition. There 

 is here a most excellent field of work open to any one who 

 may wish to cultivate it. But such problems are to be stud- 

 ied at leisure and not in the hurry of a general survey of 

 many lichen societies. Then, too, there is the hairiness or 

 ciliate condition of a number of the lichens of northern Min- 

 nesota. This finds expression sometimes as strong rhizoids on 

 the lower surface as in the Peltigeras, in the smaller ones form- 

 ing a dense nap on the lower surface as in Nephromas and in 



