122 
IOWA ACAli)E'MY OP SCIENCE 
and 8; or both may appear, as in figure 7. The first of these 
types is the most common. 
The grouping of the xerophytic adaptations in the several 
species is brought out in the table which/f ollows. It will be no- 
ticed that this grouping is quite irregular. 
' The following list contains the names of the plants which 
were specially studied. The Eoman numerals at the heads of 
the columns apply to distinct xerophytic characters, and when 
the character is present it is marked with a plus sign. The 
explanation of the Roman numera;ls follows: 
I. — Reduced leaf surface. 
II. — The rosette habit. 
III. — Large roots. 
IV. — Spines or prickles on sur- 
face. 
V. — Surface hairy or scaly. 
VI. — With poisonous or offensive 
properties. 
VII.— Milky. 
VIII. — Tissues compact, with 
small intercellular spaces. 
IX. — With thick cutin. 
X. — ^Water-storage tissues, of 
the parenchymatous type. 
XI. — Bulliform cells — water-stor- 
age. 
XII. — Sunken stomata. 
XIII. — Elongated palisade cells. 
It is evident that the structural modifications of the prairie 
plants are distinctly xeromorphic, with considerable variation 
in the particular grouping of these characters. 
