1222 Wisconsin Academy of Sciences , Arts and Letters. 
1905 and 1910. 'In the arrangement of genera and species, 
again I have followed Macbride. 
I desire to make grateful acknowledgment to Dr. Robert. A. 
Harper, first for suggesting to me this most enjoyable subject 
for study, and second for his invaluable advice and assistance 
in the work during the first three years; to Dr. Charles E. Allen 
for help during the past year; to Dr. Thomas H. Macbride for 
assistance in determining several difficult specimens; and to 
various members of the Department of Botany of the Univer¬ 
sity of Wisconsin for assistance in collecting material. 
