180 



IOWA ACADEMY OF SCIENCES. 



quently quite bare of them. In the Iowa region the old boards 

 are abundantly supplied with lichens, even in dry places. 



The reconstructed Stable below (which leaves the numbers of 

 lichens for the substrata considered unchanged in the Minne- 

 apolis column except that for the earth lichens all calcareous 

 earth lichens plus all earth Gladonias are omitted, treats the 

 Fayette earth lichens in the same way and also deducts from 

 the latter column all the calcareous rock lichens found on sur- 

 face exposures) gives the relative per cents for all the sub- 

 strata considered as influenced by atmospheric conditions 

 alone: 



SUBSTRATA. 



NO. AND PER CENT, FAYETTE 



NO. AND PER CENT, MINNE- 

 APOLIS. 



Wood 



Calcareous rocks 



Granite rocks 



Earth . 



90 or e8+ per cent 

 20 or 15+ 

 17 or 12 8— '« 

 5 or 4— " " 



58 or 62 3 + per cent. 

 17 or 18 25- 



12 or 12.8+ 

 6 or 6 5— 



This table simply places the per cents that would result from 

 atmospheric conditions where they may be easily compared. 

 However, by the reduction of the numbers representing earth 

 and calcareous-rock lichens to eliminate other causes, it reduces 

 the advantage for the Minneapolis vicinity in granitic rock 

 species to a very small fraction. A somewhat larger number 

 of such rocks were examined about Fayette, and possibly the 

 larger number increases the number of species of lichens on 

 them, which once established may now all be found on a few 

 of the rocks. However, if the smaller number about Minne- 

 apolis is due to removal of the rocks, this argument loses much 

 of its value. This table shows the relation between the wood 

 lichens, as influenced by climate alone by per cents, which has 

 not been done before. 



The Saint Peter sandstone along the Mississippi river near 

 Minneapolis, and that along the same river in northeastern 

 Iowa, near McGregor, may be compared as to lichen-floras by 

 use of the following table, which gives the species character- 

 istic of these rocks in both places, and also those found on 

 them in each place and not in the other: 



8PEOK8 FOUND IN BOTH 



PUCES 



Ramallna calicaris (L.) Fr. 



v.-ir F^rinacea Bchser. 

 Urceolarla scruposa (L.) 



Nyl. 

 Cladonia cornucoploides (L ) 



Fr. 

 Usnea barbata (L.) Fr. var. 



ruhlglnea Iftlchx. 



NORTHEASTERN IOWA 

 ONLY. 



Pannaria microphylla (Sw.) 

 Delos. 



I donia ranpiferina (L ) 



II tl'm v;ir Svlvatica L. 

 Oladonia uncialls (LJ Fr 

 Blatora granulosa (Ehrh.) 



Poetsch. 



ABOUT MINNEAPOLIS ONLY. 



Oladonia ctesplticia (Pers.) 

 PI. 



