158 



The Plant World. 



200 and 300 years were not uncommon in the flood plains of 

 many of our streams. West of the Des Moines basin the country 

 is m.ore undulating and the Missouri loess becomes more evident. 

 The flora, too, changes. It is characterized by the invasion of 

 some western species like Aplopappus spinulosus, Etiphorhia 

 marginata, Gaura coccinea; in northwestern Iowa the Ment- 

 zelia ornata, Cirsium canescens. The most conspicuous plant, 

 however, is the yucca (Yucca glauca) which becomes more com- 



Fig. 3. Lodge Pole Pine (Pinus Murrayana) and Subalpine fir 

 below t.mber line, near Petersen, Utah. Elevation 9000 feet. 



m~in westward, especially as we reach the Rocky mountains. 

 In Iowa it usually bloo ns in June or early in July, but it is in its 

 pri ne in the foothills of the Rockies the latter part of June and 

 early in July. The pendant more or less bell-shaped yellowish- 

 white flowers hang in ample racemes and make a fine display in 

 the otherwise monotonous landscape. The species is abundant 

 about Manitou and Colorado Springs and on the west slope near 



