142 IOWA ACADEMY OF SCIENCES. 



two usually from different individuals, the reasons for much 

 of our difficulty and confusion become apparent. Not that 

 such a complete specimen as has just been defined is always 

 necessary in order to accurately determine any given plant in 

 hand. Far from it. And besides it is impossible for the gen- 

 eral collector to secure complete specimens. But such com- 

 plete specimens, and many of them, are necessary before we 

 can establish the limits of variability in individuals, in varie- 

 ties, and in the species themselves. 



In my studies of the willows of Iowa, I have been afforded 

 much assistance by the botanists and plant lovers of the state. 

 The work was begun, and nearly completed, in the laboratory 

 of the department of botany of the Iowa State college, where 

 much invaluable advice and assistance was received from Prof. 

 L. H. Pammel. I take this opportunity to express my grati- 

 tude to the following persons, also for the use of herbaria and 

 for specimens sent: Prof. T. H. Macbrideand Prof. B. Shimek, 

 of the Iowa State university. Prof. B. Fink, of Upper Iowa 

 university, Mr. R. I. Cratty, of Armstrong, Messrs. W. D, 

 Barnes and A. A. Miller, of Blue Grass and Davenport, 

 respectively. Miss Minerva Benshoof , of Blue Grass, Mr. Ferd. 

 Reppert, of Muscatine, Mr. J. H. Mills, of Mt. Pleasant, Mr. 

 A. F. Sample, of Lebanon, Mr. L. R. Walker, of Clermont, 

 and Messrs. E. G. and W. M. Ball, of Little Rock. To Dr. 

 Wm. Trelease, of the Missouri Botanical garden, St. Louis, 

 my thanks are due for the use of the splendid herbarium and 

 library facilities of that institution. 



Several local floras, lists of trees and shrubs, etc., have 

 mentioned the occurrence of various species of Salix in Iowa. 

 (A bibliography will be found at the end of the paper.) How- 

 ever, no localities have been recorded or mapped in this paper 

 on the strength of these references. Every locality herein 

 given is based on actual specimens determined by the author 

 and now contained in oue or more of the various herbaria in 

 the state. In the locality lists under each species, the letters 

 "S. U. L, " following the collector's name, indicate that the 

 specimen is in the herbarium of the State university of Iowa. 

 ' ' Herb. ' ' indicates the private herbarium of that collector. All 

 specimens, not otherwise designated, are in the herbarium of 

 the Iowa State college, Ames. The numbers immediately fol- 

 lowing the localities in the lists correspond to the numbers on 

 the maps. 



