44 
sclerotia. The aethalia likewise retain the color of the plasmo- 
dium, but have the texture of dried glue and are somewhat 
wrinkled, like dried prunes. And when the sporangia are fully 
formed, occasionally one finds evidence of arrest in the presence 
of small immature spores and giant spores, four or five times the 
size of normal spores. 
Besides these arrested developments, the rapid evaporation 
seems to be responsible for the unusual position of the sporangia 
of many species. Except for the aethalial species already 
mentioned and one collection of Physarum didermoides vat. 
lividum, all specimens collected, representing some eighty species, 
were found on the under side of the support to which they were 
attached. While this is a normal position for some species, it 
is quite unusual for others. This position, often in actual contact 
with the soil, makes the organisms peculiarly liable to attack by 
molds. This is noted in superficial growths upon the sporangia 
at the time of collection and in the appearance of mold spores 
carried up into the sporangium by the rising plasmodium. When 
sclerotia are reanimated in the laboratory, these molds, which are 
peculiar to the forest and are not the forms usually seen in the 
laboratory, often get the start of the plasmodium and prevent 
further development. 
SuMMary.—In the district investigated the occurrence of 
myxomycetes is strictly limited by the continuance of an available 
supply of water through a definite minimum period. The optimum 
conditions for their occurrence are found in mountain valleys and 
wet wooded hillsides at elevations of 8,000 to 9,000 ft. 
There is some restriction in the occurrence of species due tO 
the limited number of tree species in the area. ; 
Certain species are found in drier locations where a definite 
type and degree of decay is present in fallen logs of conifers. Cer- 
tain aethalial species found in dry locations get their food an 
moisture from dead or living trees affected by heart-rot. 
The rapid evaporation from all exposed moist surfaces leads 
to arrested development at various stages of the life cycle, aen ; 
usual position of sporangia and consequent extreme susceptibility 
to attack by molds at various stages of their development. 
COLORADO AGRICULTURAL COLLEGE 
Fort CoLLINS, COLORADO 
