538 
hang on slender filaments, easily shaken by the slightest breeze. The 
spikes are so arranged that when acted upon by the wind they turn 
like vanes, This brings all the spikes in a direction nearly parallel 
to the wind, the stigmas being to windward and tie anthers to lee- 
ward: thus the stigmas necessarily receive pollen from a different plant. 
The same adaptation is seen in other species of Bouteloua and in some 
other grasses. 
The following species are also frequent in the uplands: 
Ailionia linearis. Tpomeca leptophylla, 
Ambrosia psilostachya. Lacinaria punctata. 
Artemisia wrightit. Lepachys columnaris. 
Asclepias latifolia. Linum rigidum, 
Carduus ochrocentrus. Lygodesmia juncea. 
Engelmannia pinnatifida. Meriolix serrulata. 
Mriocarpum spinulosum., Psoralea tenuiflora. 
Evolvulus nuttallianus, Solidago miszsouriensis. 
Grindelia squarrosa. Sophora sericea. 
Gutierrezia sarothra, Thelesperma gracile, 
Tymenopappus tenuifolius. 
All these are adapted to the dry climate by possessing the power to 
retard evaporation from the foliage. Many of them have small or nar- 
row leaves, as in Allionia or Lacinaria, or the leaves are deeply lobed 
or cut, as in Hymenopappus and Thelesperma, or compound with small 
leaflets, as in Sophora. In Ambrosia awrightii the narrow lobes of the 
leaves are strongly revolute. The surface is often covered with a hairy 
coating (Evolyalus, Engelmannia), or is resinous (Gutierrezia, Grin- 
delia). Grindelia, moreover, is strongly paraheliotropic, the sessile 
leaves twisting near the base and assuming a vertical position. In 
Linum and especially in Lygodesmia the leaves are reduced, the rod- 
like stems acting as foliage. Asclepias latifolia is the only plant with 
broad leaves. The leaves, however, are thick, and are either so 
arranged that they are shaded when on the opposite side from the sun, 
or set at such an angle as to present the edge to the sun. They are 
also set close together, so that they protect each other from rapid 
evaporation. Furthermore, the contiguous lobes at the bases of the 
leaves, which are opposite and sessile, are upturned, thus forming % 
depression near the base of each leaf, in which water collects after a 
‘ain or a dew at night. This water will remain for many hours and 
doubtless serves to modify evaporation. 
Mr. Thompson collected no Cacti. There are three species common on 
the uplands: Opuntia mesacantha, with pink, pulpy fruit which is eaten 
by small animals; O. polyacantha, with smaller joints and small dry 
fruit; and Cereus viridiflorus Engelm. The two species of Opuntia 
when found on the uplands almost always have the joints in a vertical 
position, but appressed to the ground. The tufts of joints are thus 
not raised much above the buffalo grass. When they oceur in the 
bottom land, as is frequently the case, many of the joints are lifted 
from the ground and often present the side to the sky. 0. polyacantha 
