70 
from the effects of that fungus, even to the naked eye. In many in¬ 
stances the openings in the almond leaf are bounded by the finer veins 
or vascular bundles. The midrib is rarely divided by Gercospora , and 
the larger secondary veins often prove an obstacle to its extension. In 
some instances cells are formed about the infested tissue of these cir¬ 
cles apparently as a protective provision, and they are perhaps compar¬ 
able to the transverse cells cutting off leaf petiole and blade when of 
no further use to the plant. More observations are needed to determine 
if this growth be common or exceptional. Where infection occurs near 
the margin of a leaf the opening left is semicircular, and resembles the 
work of the leaf cutter bee, Megachile. The outer effects of this fungus 
on the leaf are figured (Plate xi, Figs. 1, 5, 6). Figs. 5 and 6 are of 
the almond leaf, and represent the greater part of a leaf of natural size, 
with a smaller portion enlarged about 3 diameters. Fig. 1 is of a peach 
leaf badly infested by Gercospora , also natural size. 
We learn through a study of the leaf tissues that all portions are 
involved in the effects of Gercospora’ circumscissa. The vessels are filled 
with a reddish, amorphous, gum-like deposit, the entire vascular bundle 
being involved in the discoloration. The compact upper palisade cells 
are shrunken and wanting in chlorophyll and amylaceous material; and 
this is also true for the lower, more openly arranged palisade cells or 
spongy parenchyma. The cell walls are yellowish, while the cell lumen 
usually contains a yellowish granular deposit in greater or less abun¬ 
dance. So far as observed, most of the chlorophyll bearing cells have 
their walls uninjured. 
DISSEMINATION OF THE DISEASE AND PREVENTIVE MEASURES. 
The small circular pieces of diseased tissue excised from the leaves 
of affected plants unquestionably provide for a ready spread of the 
disease. They bear near the center of one or both surfaces fascicles of 
abundant conidia. Prior to their fall from the leaf, these pieces of 
tissue commonly warp into the form of a watch crystal or even a cup. 
Moderately warped pieces are shown in cross section in Figs. 7 and 8, 
of Plate xi. The margin of the piece may warp either upward or down¬ 
ward, but in either case many fascicles of conidia are protected at the 
center of the concave surface from the touch of most external objects. 
The diameter of the cup-shaped pieces varies from 1 to 6 millimeters, and 
they may protect from one hundred to several hundred conidia. The 
spores arising from the convex surface are soon freed and scattered. 
Those within the conca vity are retained much longer and until the pieces 
m ay be blown or carried by the water of irrigation for long dist ances. Un¬ 
questionably both the minute size and peculiar shape of the spore-bear¬ 
ing tissue greatly facilitate the dissemination of spores. Water readily 
separates the mature conidia from their conidiophores, and in case of a 
light shower they are freed and distributed over surrounding foliage in 
