l62 UNIVERSITY OF COLORADO STUDIES 



ties. Particular mention may be made of the loco weeds^ which occur 

 on plains and bluffs. Another plant of this family, a species of Pso- 

 ralea,'^ is the dominant plant on the mesas and ridges and much of the 

 plains formation in early summer. It has somewhat the appearance 

 of sweet clover or alfalfa but grayish in color and with few leaves. 

 Along with the Psoralea are found one or more shrubby species of 

 wormwood. 3 



Well-developed river-bottom forests'* occur along the St. Vrain 

 Creek below Lyons and especially along the Poudre River near Windsor 

 there is some fringe of forest^ accompanying all of the water courses. 

 At the first point named above the trees are chiefly narrow-leaf cotton- 

 woods with some western cottonwoods.*^ Other trees are small birches,' 

 alders^ and box-elders.^ The Poudre forest is made up of the common 

 western cottonwood together with box-elders and two or three willows. 

 Here there is often a dense undergrowth of rank herbs and such trailing 

 and creeping plants as hops, clematis and Virginia creeper^° and 

 poison ivy." 



The total number of trees and shrubs in the region studied is small. 

 Besides those species which occur in river bottoms there are certain 

 trees which grow only on the bluffs and near the heads of gulches. An 

 especially interesting place is the bluff at the southern limit of the high 

 plains about eight miles west of Pawnee Buttes. Here the western 

 cedar" was found and also one of the five-leaved pines. '^ The occur- 

 rence of the latter is particularly noteworthy as this tree has not been 

 reported in Colorado except from high mountain stations. The shrubs 

 growing along these bluffs are the skunk bush^-* and the mountain 

 mahogany. '5 Following is a list of all the woody plants collected by 

 members of the party. 



' Species of Astragalus and AragaUus. ' Acer negundc Linn. 



' Psoralea tenuiflora Pursh. "" Parlhetwcissus vitacea Hitch. 



3 Artemisia. " Rhus rydbergii SiaaW. 



* See Fig. 3, Plate I. " Juniperus scopttlorum Sargent. 



5 See Plate II. '' Probably Pinus fiexilis. 



' Populus sargentii Dode=P. ouidcntalis (Rydb.) Britt. '* Rhus trilobata. 



7 Betula loniinalis Sarg. »s Cercocarpus parvifolius. 



8 Alnus tenuijolia Nutt. 



