Certain Fungi Parasitic on Plants. 
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of a plum tree, in which sections of the sphaeria ( perithecia ) are 
exhibited highly magnified, while the woody fibre is represented 
of the natural size, as seen by the naked eye ; in its advanced 
stages its woody structure appears as if it had been broken up 
into shreds and its interstices partly filled with a very porous 
bark-like substance, which is again interspersed with a very 
fine transparent thread-like mycelium ; 5, a typical representa- 
tion of a perithecium ; 6 a, Plate XCVI., a very highly magnified 
translucent view of a perithecium partly covered with branches 
(flocci). Its surface is cellular, as exhibited, and of a dark amber 
colour. The flocci is jointed and branched, and resembles very 
much black-orange mycelium. I have found floating in the gum 
solution, when examining the respective parts of black-knot, several 
small forms resembling Cladosporium, having very short stalks, 
and of the colour of the perithecium and its flocci. This led me to 
renew my experiments. I placed on slips of glass crushed portions 
of perithecia and their flocci, and exposed them within glass jars 
containing about an ounce of water, securing the contents with 
ground stoppers. I then subjected them to a temperature of about 
75° Fahr. for a period of fifteen days. After many trials of this 
character I obtained several examples of Cladosporium forms 
growing on the flocci, as suspected by Peck. I endeavoured 
to secure the specimens under glass with a gum solution in 
the usual way, but the moment the fungus was wetted with the 
gum water, the Cladosporium forms separated from the flocci. 
I have since frequently endeavoured to restore all the conditions 
necessary to produce the visible combination of the flocci with 
these forms, but have thus far failed, although it is common to 
find them floating on the glass slides. When a branch, such as that 
represented by Fig. 1, Plate XCV., is bleached by the alternate 
action of nitric acid and chlorinated soda, the parts covered with 
the fungus are freed from it : I find it exists mostly on the surface 
of the excrescences. A microscopical examination of the mass will 
show that it is almost wholly composed of woody tissue, vascular 
bundles, &c., and seems void of earthy matters, and is very delicate 
in texture. That portion of the branch which appears unaffected 
by the fungus remains as firm as if it had not been treated with 
chemicals. It would seem that this fungus produces an irritation 
on the surface of the branches, from which masses of perfectly formed 
cellular structure then burst out, preventing the growth of con- 
solidated wood. It is generally supposed that when black-knot 
encircles a branch it dies from compression, whereas black-knot, so 
called, consists of exudations of organized pure cellulose, on the 
surface of which black-knot fungus principally grows. The sub- 
stance of the exudation is closely approximated to starch and sugar. 
This may account for its having been so frequently made the abode 
