NORTHERN COLORADO PLANT COMMUNITIES 229 



Gravel slide plants are found wherever there is much weathered and 

 disintegrated rock. In the course of time a talus slope may produce 

 enough vegetation to allow an accumulation of soil. Limber pines and 

 lodgepole pines will then find their way into the formation and even- 

 tually it becomes converted into a part of the general coniferous forest 

 formation. 



The plants of sand banks and sand bars along streams are few and 

 far between because of the looseness of the soil and the rapidity with 

 which it dries out. A study of the species which first occupy such 

 situations and the changes of vegetation in any such piece of ground 

 would make an interesting little piece of work. 



Aquatic vegetation represented in the ponds and streams of Boulder 

 Park is somewhat varied. It might be classified into formations and 

 associations. The most conspicuous seed plants are species of bur 

 reed (Sparganium). Algae are numerous. The student should consult 

 Schimper's Plant Geography and Warming's Ecology of Plants for 

 detailed accounts of the formations of aquatic plants. 



The Alpine Formations at Rollins Pass (Corona, Colorado) 



Although 20 miles by rail from Tolland the top of the pass is only 

 about 8 miles in a straight line. The elevation is 11,660 feet, the top of 

 the ridge above the railway station about 12,000 feet. A true alpine 

 climate is encountered here as is shown by the United States weather 

 records. The July temperature is about 47 degrees Fahrenheit, or 22 

 degrees lower than the July mean for Denver. The climate can, of 

 course, be judged very well by the plant population. It appears that a 

 few species found on the high peaks adjacent are here absent but the 

 plant formations and associations are the same as occur on the highest 

 mountains in the vicinity. 



Little need be said of the pond vegetation of the alpine districts, indeed 

 very little is known about it. There are some algae and a very few seed 

 plants found in the cold waters of the lakes above timberline. 



Considerable areas of dense alpine scrub formed of willows 2 to 4 feet 

 tall occur on the high ground above Corona Lake and in places through- 

 out the alpine zone. A scrub formation of wind-blown Engelmann 



