PAPERS ON BOTANY 129 



Some 54 examples of peculiar distribution are here cited with 

 reasonable explanations of the same where explanation is ap- 

 parent. The author admits that some of these explanations 

 are possibly open to criticism and invites the same with the 

 hope expressed that it partake of a friendly helpful nature. 

 These examples are given in the order of their natural se- 

 quence from lower to higher forms. In a great majority of 

 the examples named the stations are unique, in that the plants 

 were found there and there only in the three counties. This 

 very isolation renders the cases of distribution more interest- 

 ing, and at the same time more difficult of explanation. To 

 avoid continual repetition, the letters appended refer to the 

 proposed explanations given in the conclusion and summary. 



1. Pellaea atro purpurea, the rock brake, is found in the 

 deep stone "cuts" of the Illinois Central railway west of 

 Warren, probably five miles from any natural stations which 

 lie south and west. Also in similar cuttings southeast of 

 Freeport, 30 miles distant and nearly 40 miles from natural 

 outcrops. N. W. of center of Distribution (D. C? or A?) 



2. Woodsia obtusa, in the famous rock cut of the St. 

 Paul railway, north of Warren. One clump only. No other 

 stations known for the species in Jo Daviess. N. W. of center 

 (D). 



3. Botrychium obliquum, one plant on the Niagara lime- 

 stone summit of Benton Mound. No others ever found nearer 

 than 10 miles. Only the one station ever discovered in Jo 

 Daviess. (G). 



4. Azolla Caroliniana, exceedingly abundant along Liver- 

 pool road in Illinois River bottoms of E. Fulton, the only 

 station where the plant has ever been seen, in all of the author's 

 botanical tramps. (G). 



5. Tripsacum dactyloides, on an alluvial border below 

 Seville, Fulton county, the only station; along the northern 

 limit of range. (C). 



6. Acorus Calamus, Sweet Flag, in isolated and far sep- 

 arated patches here and there in all three counties. The 

 writer hazards the theory that this peculiar distribution, en- 

 tirely absent in countless suitable places, is due in large part to 

 Indian planting. (B). 



