74 
Mycologia 
preservation afforded by the accumulations of amber at a time 
long subsequent to the Carboniferous have given us a glimpse of 
some few fungal types of the older Tertiary. 
In the examination of a large series of petrified woods (the 
majority of which are of Tertiary age) for the United States 
Geological Survey, I have frequently noted the ravages of para- 
sitic fungi as well as branching mycelia of both septate and non- 
septate hyphae. Most of these are too indefinite for incorpora- 
tion ,in the record, but it may be safely concluded that fungi were 
obviously as abundant then as now, and among the remains dis- 
covered several are so exceptionally well preserved that their de- 
scription becomes important to both the botanist and geologist. 
The first of these may be called Peronosporoides palmi sp. nov., 
not so much because T am certain that it is related to the modern 
genus Peronospora, but because it resembles various living species 
in that genus and I believe is clearly referable to the Peronospora- 
cese. It may be described as far as the nature of the material 
permits as follows : 
INIycelium intercellular, freely branching, with fused cross 
branches. Hyphae thin, .0025 mm. to .00375 diameter, 
profusely septate, the lengths of the cells variable, no clamp con- 
nections observed. Oogonia intercellular, numerous, relatively 
large, spherical, terminal, about .0357 mm. in diameter. Antheridia 
somewhat smaller, about .0238 mm. in diameter, subspherical. 
Objects having all the appearance of oospores or zoospores are 
distinctly visible in some of the ooginia. PI. 180, f. 2, shows two 
partially collapsed antheridia in conjugation with oogonia and the 
oogonia which are interpreted as containing oospores are found in 
those oogonia as in PI. 180, f. 3, where the antheridium is com- 
pletely collapsed and only a trace of it is left or where it has 
entirely disappeared. 
This form is exceedingly abundant and beautifully silicified in 
a small stem (about 7 cm. in diameter) of Palmoxylon cellulosum 
Knowlton from the lower Oligocene of Mississippi. Oogonia and 
antheridia are plentiful both in the broken down fibro-vascular 
bundles and in the intercellular spaces of the parenchymatous 
ground mass of the stem. Several of the oogonia show what are 
clearly to be interpreted as spores and after making a careful 
survey of the literature I feel justified in asserting that this is the 
