108 
IOWA ACADEMY OF SCIENCES 
General Characters. The fungus appears on the leaves in July at 
first causing somewhat round, yellowish spots which later become con- 
fluent and assume a greyish or bluish cast. Occasionally the greater part 
of the slightly swollen leaf may be involved. The fungus fruits on both 
sides 'of the leaves perhaps more frequently on the lower; but Dr. Robin- 
son states that in Quercus tinctoria he observed asci only upon the upper 
and the same observation has been made by the writer in the examina- 
tion of the Rocky Mountain Oak, Quercus undulata. 
Microscopic Characters. The vegetative mycelium is sub-cuticular 
and gives rise to the asci. They are club-shaped, rounded at the top, 
without stalk-cells, but have one or more root-like processes which pene- 
trate between the epidermal cells of the host; they vary in size from 
18-23" X 45-78". Are very numerous and rod-like very variable, 1-3-4-7 1-4", 
This fungus is without doubt common in the Rocky Mountains, but owing 
to the investigations of the writer being made rather late in the seasons 
of 1900 and 1901, good material was not then procured. He, however, col- 
lected it in 1895; on Quercus undulata var. gunnisoni, in the front range 
in the vicinity of Colorado Springs, where it is abundant. 
ERYSIPHEAE, Lev.^ 
The mildews are widely distributed fungi producing troublesome dis- 
eases of the grape, many herbaceous plants, and not a few of our trees. 
The more important of the species affecting trees are the following: Phyl- 
Jactinia guttata which occurs upon Fagus, Carpinus, Corylus, Crataegus 
Castanea, Quercus and many other shrubs and trees, and has been reported 
by Anderson^ upon Betula occidentalis and Typha latifolia: Podosphaera 
oxyacanthac upon various species of Prunus, Spiraea, Pyrus, Crataegus, 
Amelanchier and Diospyros, the latter host being reported by BurrilP. 
Microsphaera. alni upon many different hosts, especially Carpinus 
caroliniana, Betula, Cornus, Vidurnum, Syringa, Celastrus, TJlmus and 
Juglans; M. elevata on Catalpa speciosa and C. bignonioides ; M. quercina 
upon the various species of the Quercus or oak, as Q. alba, Q. macrocarpa, 
Q. bicolor, etc.; M. calocladophora, Atkinson upon Quercus aquatica and 
Q. lauifolia, M. erineophila. Peck; Erysiphe liriodendri upon Lirioden- 
dron tuUpifer'a; SpJiaerotheca mali upon the apple and S. phytoptophila, 
Kell. & Swi. upon the hackberry, {Celtis occidentalis)-, S. lanestris on 
(Q. agrifolia). 
The mycelium of these fungi vegetates on the surface of the plant, 
where it forms branching, septate, usually white and much interwoven, 
threads which abstract nourishment by means of little haustoria or 
suckers that are sent into the epidermal cells. The reproductive bodies 
are called conidia and are single, colorless, cylindrical, either oval or 
ovate, they are attached end to end in chains of somewhat elongated coni- 
diophore^. Perithecia arise from the mycelium and are the result of 
fertilization. They are usually globose, but occasionally are slightly 
flattened, at first colorless, finally brown, or in some cases when mature, 
T. Ann. Sci. Nat. III. 15: 109-179. pi. 6-11. 1851. 
2. Ellis & Everhart. N. Am. Pyrenomycetes. 21. 
