IOWA 'ACADEMY OP SCIENCE 
27 
but from our knowledge of the effect on small trees, we may conclude that the 
lumber quality is destroyed, hence an economic loss, as it is being used very 
extensively for building purposes. For this reason this fungus is one of the 
most important economically of any of the species under consideration. 
Pyropolyporus fulvus: This fungus affects only the diseased trunks of 
various species of Prunus and is widely distributed over North America and 
Europe. In Plant Diseases in 1907 it is not mentioned. 
The fruiting bodies of this polypore vary in size from 1 — 6 inches long, 
^ 2 — ^2 inches broad, by 14 — 11^ inches thick. They form large masses when a 
large number are joined, as in some instances several limbs or main branches 
are covered with sporophores. The fruit bodies are elongated usually resupi- 
nate, very hard, edges nearly black, while the fruiting surface is a dark brown. 
This fungus does not grow in shelf form, but horizontal to the tree, leaving 
the concentric ridges only visible at the very edge of the sporophore; and 
frequently as resupinate forms coalescing in a series. The hymenium consists 
of regular pores of rounded minute openings. It is a perennial growth, hence 
tiny moss plants may be found growing upon it. 
The condition favoring spore entrance is a wounded area. It has been ob- 
served that the sporophores are more common on the branches than on the 
trunk, and it has the appearance of working from the top downwards. Upon 
removing one of these sporophores no wounded' area is visible, yet there are 
some located near a broken limb. Hence we conclude that it was through this 
broken limb that entrance was gained. 
A cross section of a diseased branch shows that it is thoroughly infected, 
rendering it very brittle, while normally it is tough. Again the alternate area 
of light and dark wood prevails too near the sap wood. Prom these noticeable 
features . it appears to attack only definite tissues or else follow the annual 
growth. 
Its favorite host is the wild plum, and a few specimens have been observed 
on cultivated trees when pruned. One wild grove in particular where speci- 
mens were gathered, there was not a tree unaffected and most of them were 
dead. It appeared also that the cluster in the timber is much more subject to 
attack than those in the open, which might be explained by the former being 
more conducive to infection due to more moisture. Also the question arises 
if the fungus is strictly parasitic, for I believe specimens were gathered on 
dead hosts. If it be true mat a plum supports this fungus long after its destruc- 
tion, it is more tenacious of life than Pyropolyporus igniarius as the sporophore 
ceases to grow at the death of the host. Among the plums there is a greater 
proportion of diseased trees than any other yet studied. 
The economic importance of this parasitic disease lies not in the fact of the 
commercial value of the wild plum, but in the tendency to infect the tame ones. 
Then it would have an economic importance for the fruit growers. 
Elfvingia megaloma: The last fungus for consideration is Elfvingia mega- 
loma, which is widely distributed over the United States and Canada. It is 
reported from Nebraska by Dr. Heald as parasitic upon cotton wood; like- 
wise by D’Allemend from the same state under the name of Fomes appTanatus 
parasitic upon cottonwood. As a parasite it attacks the red oaks in this region, 
but has not been found on the cottonwood; as a saprophyte it is found on dead 
trees, stumps and logs. 
