242 FOLIICOLOUS SPH ERLE. 
pared together, and no species has been proposed as new which has not 
been examined independently by both in order to guard against errors 
of observation. The measurements are expressed in decimals of the 
French millimetre, on account of its more universal use (Great Britain 
excepted) and its superior advantages over a higher unit such as the 
English inch. To meet any objection that microscopists in this country 
have little knowledge or experience of millimetric admeasurements, 
the equivalent in decimals of an inch has in many cases been added. 
One of the first difficulties which beset our examination, was the de- 
termination of the Spheria maculaformis of Persoon. We found also 
by experience how often maculeeform Spheria are barren long after the 
leaves have fallen from the parent tree. Two or three plants with 
similar external appearances, but with very different fruit, and ulti- 
mately others, were examined, any of which might be accepted as agree- 
ing perfectly with the description. Sometimes these occurred on the 
same and sometimes on different leaves. Neither was our resort 
to published specimens much more satisfactory, for these did not accord 
with each other, and, of two species found on the same leaf, there was 
no evidence which was to be accepted. After some months of close 
application to the same subject, and the examination of hundreds of 
specimens, we at least deserve to be free from any charge of arriving at 
hasty conclusions. 
Four plants are now described, and one or two others have been ob- 
served, but not with sufficient satisfaction to be included, as possessing 
more or less the features of Spheria maculeformis, Pers. ; that which 
we have accepted as the type is the one which appeared to us to have 
the strongest claims to be the most common, and to occur on the 
largest number of published specimens. This species (Fig. 6)— 
besides its occurrence on Oak, Elm, and other dead leaves, *' in ma- 
culam nigram inequalem conglomeratis "—is also met with scattered 
over the whole under surface of the leaves of Castanea vesca, but, as 10 
difference save that of habit could be discerned, I have regarded it 
as a variety, under the name of centigrana, Another variety was ob- 
served, having both cells of the sporidia equal, which I have only 
recorded as a variety, under the name of equalis. 
Of the species resembling the above, the nearest is S. oblivia, which 
occurs in groups or clusters on the under surface of the leaves of Ons- 
tanea vesca. The points of difference are chiefly in the fructification. 
