6 A Handbook of Nebraska Grasses. 
The present key includes most of the species known to occur 
in Nebraska, tho a few of minor importance and very restricted 
distribution have been omitted. There are provided also some 
data on the economic value of certain of the most important 
species. 
The illustrations for the grass keys have been drawn expressly 
for this publication. They are derived in part from actual 
authentic specimens and in part redrawn in modified form from 
various manuals and monographs. The authors have made free 
use of the manuals, monographs, etec., included in the Bibli- 
ography and take this opportunity to commend these publications 
to the attention of all who wish to learn more of our common 
erasses. It is hoped that the keys here presented will facilitate 
the study of the grass flora of Nebraska by farmers and students. 
STRUCTURE OF GRASSES. 
The grasses are herbs (rarely shrubs or trees) with extensive 
fibrous root-systems. They may be perennials with rhizomes 
(fig. 1, A) or sympodia (fig. 1, B), or annuals with sympodia. 
The extensive system of rhizomes enables these plants to form 
a “sod” and may render their eradication difficult. The primary 
root soon disappears, its function being taken over by numerous 
secondary roots which arise from the nodes. 

Lees abe 
They have cylindrical stems with hollow internodes 
and generally swollen closed nodes (fig. 2). In some 
species, such as maize and sorghum, the stems are filled 
with pith. 
The leaves are 2-ranked, narrow, parallel-veined (tig. 
3) and consist of two parts, the sheath (fig. 3, C) and 
the blade, (fig. 3, A). The sheath with its margins over. 

