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III. — Certain Fungi Parasitic on Plants. By Thomas Tayloe, 
Microscopist of the United States' Department of Agriculture, 
Washington, D.C., U.S.A. 
Plates XCV., XOVI., and XCVII. 
(1) Black-Knot. 
Entomologists and botanists are now generally agreed that the 
black-knot of cherry and plum trees is produced by a fungus, but 
they have failed thus far to define sufficiently its internal and 
external structure. Schweinitz, the American botanist, who died in 
1834, seems to have been the first who suggested its fungoid origin, 
and he named it Sphmria morhosa. During the past year the Hon. 
M. P. Wilder, of Boston, forwarded a specimen of the black-knot 
on a plum-tree branch, which I used as the basis of my experi- 
ments. The ordinary methods of investigating the black-knot by 
placing opaque sections of it under the microscope gave results so 
unsatisfactory that I determined to employ my usual methods of 
rendering such bodies translucent and soft, by means of acids and 
alkahes. In this way the higher powers of the microscope may be 
brought to bear efi'ectively on the fungus, its mycelium, flocci, and 
spores, if present. The immediate use of strong mineral acids 
and caustic alkalies on suspected fungoid bodies has this advantage, 
that these prevent the possibility of the production of fungus growth 
by fermentation during the investigation. Portions of the black- 
knot were subjected to the action of nitro-muriatic acid (concen- 
trated) during several days, after which the acids were neutralized 
with ammonia. This process rendered the outer surface of the 
sphaeria translucent, and I then examined them under low and high 
powers of the microscope. Portions were also well washed in pure 
water, to free them from acid, and then submitted to the action of 
caustic potash. For the purpose of distinguishing colourless spores, 
mycelium, starch, and cellulose from one another, a solution of 
iodine, containing a small portion of nitric acid, was applied in 
excess to the specimens, and afterwards washed in pure alcohol. 
This - solution stains starch blue, fungoid cells a light amber, in- 
fusorial matter a dark amber, while cellulose remains generally 
colourless. When viewed under a power of 100 to 600 diameters, 
these substances are clearly distinguished from one another. I also 
submitted the dry leaves of the twigs to the same processes and 
examined their transparent cellulose forms carefully, and observed 
some indications of fungoid forms within the cells of the leaves. 
Fig. 1, Plate XGV., represents the general appearance of the 
black-knot of the plum ; 2, a cross section ; 3, an enlarged view of 
it, showing indentations on the external upper surface of the 
sphaeria ; 4, a longitudinal section of the black-knot and branch 
