Ecological Observations on Colorado Myxomycetes 
Ernest C. SMITH 
Five years of intensive collecting of myxomycetes in north- 
eastern Colorado have impressed upon the writer certain features 
of the distribution and behavior of these interesting organisms. 
Here, as elsewhere, the factors limiting occurrence are the avail- 
able supply of water and of decaying vegetable matter, but these 
factors have certain peculiar features in the region considered and 
affect not only the distribution but also the behavior. 
While Colorado is described as “semi-arid” and the reported 
occurrence of one hundred and twenty-five species of Myxomy- 
cetes may cause initial surprise, this is dissipated when local con- 
ditions are known. While the plains just outside the foothills, 
with an average elevation of 5,000 feet, have an annual rainfall 
of approximately fifteen inches, a station in Estes Park at an 
elevation of 8,000 feet has an annual rainfall of twenty-three 
inches, while Palisade Lake, elevation 10,000 feet, has forty-eight 
inches. Even more significant is the fact that in a given locality 
more than 50 percent of the annual precipitation frequently oc- 
curs within a period of three months. 
But adequate rainfall does not necessarily furnish the right 
conditions for the growth of myxomycetes, this being only one 
of the factors concerned. The supply of moisture must be con- 
tinuous through a considerable period of time, and decaying vege- 
table matter must be present. In the mountains, where the rain- 
fall is greatest, the ability of the soil.to retain moisture is de- 
termined by the slope of the ground, the exposure, and the forest 
cover. The optimum conditions are found in this district at 
scattered stations at elevations from 8,000 feet to 9,000 feet on old 
glacial melting plains where beaver-dams have helped to create 
wooded Swamps, or on wooded hillsides kept moist by seepage 
from Springs, beaver-ponds or melting snows. Precisely these 
locations also provide the decaying vegetable matter which is the 
Second desideratum. This is an important point, for even in the 
mountains, acres of down timber frequently fail to yield a single 
log with the type of decay favorable to the presence of myxomy” - 
cetes. - 
Again, these mountain districts support a limited number of 
tree species—three pines, two spruces, Douglas and subalpine firs, 
aspens, cottonwoods, box elders and alders. This affects both the 
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