6 111 i: FLORA OF NEBRASKA. 



find many cases of progressive simplification in following genetic lines. Grasses and 

 sedges, while in many ways simpler than lilies, are in fact much farther from the primi- 

 tive monocotyledonous type. The oaks and walnuts, the willows and cottonwoods, with 

 flowers, apparently quite simple, must be given positions in a natural system much fur- 

 ther removed from the primitive types than many plants with a much more complete 

 floral structure. These principles will account for the unusual position assigned to some 

 of i lie Families in the synopsis. 



A careful study of the flora of Nebraska shows that not only are all the great 

 branches of the vegetable kingdom represented, but that of the fifteen Classes, four- 

 teen are represent^!, and that of the fifty- four Orders, forty-three are represented, while 

 of the 386 families there are representatives of about one-half. On the other band, of 

 the 175,000 species of plants now known, probably little, if auy, more than two per cent 

 occur within our borders. 



