224 MINNESOTA BOTANICAL STUDIES. 



6. Stereocaulon paschale (L.) Fr. 



7. Umbilicaria muhlenbergii (Ach.) Tuck. 



8. Umbilicaria pustulata (L.) Hoffm. 



9. Endocarpon fluviatile DC. 



10. Parmelia conspersa(EHRH.) Ach. 



11. Parmelia saxatilis (L.) Fr. 



12. Parmelia caperata (L.) Ach. 



13. Physcia sp. 



14. Physcia stellaris (L.) Tuck. 



15. Physcia cassia (Hoffm.) Nyl. 



16. Leptogium lacerum (Sw.) Fr. 



17. Ephebe pubescens Fr. 



18. Ephebe solida Born. 



19. Pannaria microphylla (Sw.) Delis. 



20. Urceolaria scruposa (L.) Nyl. 



21. Placodium vitellinum (Ehrh ) Naeg. and Hepp. 



22. Rinodina oreina (Ach.) Mass. 



23. Lecanora rubina (Vill.) Ach. 



24. Lecanora cinerea (L.) Sommerf. 



25. Buellia petraea (Flot., Koerb.) Tuck. 



Comparing the lichens easily detected on islands numbers one 

 and three — those which give character to the flora — whatever rare 

 species may have escaped notice, we find that, of a total of 23 

 species and varieties on the first and 25 on the second, 19 are com- 

 mon to both islands, separated by several miles. The lists as a 

 whole show a large number of foliaceous and fruticulose species ; 

 and we evidently have not the primitive post-pleistocene lichen 

 population of these rocky islands, which indeed must have dis- 

 appeared centuries ago. It is the more remarkable that practic- 

 ally the same species have succeeded in replacing a former 

 flora on the two islands. I regret that time was wanting for the 

 study of more of these islands, and especially of some farther 

 from the shore line. The growth of larger forms of vegetation 

 is probably beginning to effect a decrease in lichen species on 

 island number one for otherwise, being larger, it should have 



