128 
June, 1889. 
Conduct ed bt Prof. F. Lamson Scribner. 
Botanist. Experiment Station, Knoxville, Tenn. 
Black-Knot of the Cherry and Plum, 
Black knot or “wart" of the Cherry and 
Plum are descriptive names of a special 
fungus disease of these trees consisting of 
knot -like or wart-like growths which appear 
on the smaller limbs as well as on the larger 
branches and sometimes even on the trunk. 
In many sections of the country, particu- 
larly in the Easteri. and Middle States, it is 
one the most serious obstacles to the suc- 
cessful culture of these fruits, for a tree 
which has once become affected with the 
knot rarely survives for more than a few 
years and it may become so badly diseased 
in a single season as to be no longer a source 
of profit. 
The fungus which causes the growth 
of the knots was described in its mature 
stage 68 years ago by the celebrated 
mycologist, Scliweinitz who, however, seem- 
ed to think that the knots were caused by 
some gall-pro- 
ducing insect 
rather than by 
the fungus 
which he foimd 
upon them. 
Many have sup- 
posed them to 
be the result of 
insect attacks 
and not with- 
out some appar- 
ent reason, for 
upon cutting 
open the knots 
one will very 
frequently find 
in them the 
larvae of certain 
insects. Several 
species of in- 
sects have been 
thus observed 
but none of 
them belong to Fisr. 158>. 
the gall-producing sorts and there is no 
longer any question as to the real cause 
being a parasitic fungus. This fungus is 
invariably found grow ing in and fruiting 
on the knots and nowhere else. The life 
history of this fungus has been very care- 
fully studied by Dr. W. G. Farlow who 
published an account of its habits and 
means of reproduction in the Bulletin of 
the Bussey Institute in 1876. Previous to 
this there was rtally very little known con- 
cerning this parasite and even now many 
of our fruit growers do not appear to under- 
stand the nature of the disease. 
Happily the cherry and plum trees in 
this section (vicinity of Knoxville, Tenn.) 
are entirely free from the black-knot but 
we have in hand some specimens, recently 
received from New Jersey, which well 
illustrate the disease in its advanced con- 
dition and show how serious it may become. 
Fig. 1585 was 
these speci- 
fairly repre- 
ternal char- 
fully devel- 
The curving 
drawn from 
mens and 
sents the ex- 
acters of the 
oped knots, 
direction of 
Fig. '591. 
or change of 
growth of the more slender branch in the 
figure, is caused by the fungus, its action 
having been to occasion a more rapid 
growth of the cells on the convex side 
which is covered by the knot. In some 
cases the knots are proportionately larger 
than those which we have drawn and in 
some of the samples they completely sur- 
round the branches. There is no bark over 
the knots excepting, perhaps, here and 
there a fragment which has been carried up 
with their growth, and surrounding the 
base of the knots, the raised and broken 
edges of the bark show that they originated 
beneath it. 
Upon a close examination of the black 
and more or less irregular surface of the 
knots the latter are seen to be densely 
covered with slightly elevated and rounded 
projections which give it a roughened or 
pimply appearance. Each one of these 
little pimples is a mature fruit of the fun- 
gus. Making a vertical 
section thro- yy. ugh one of 
the knots to- ' • • get her with 
the stem Fig. 1592. which bears 
it we find that within the thin black layer 
that covers the surface is a mass of spongy 
and more or less porous tissue which evi- 
dently has its origin in the cambium layer, 
the living, growing layer bet veen the wood 
and the bark. There is little or no discol- 
oration or malformation of the wood. In 
some of our specimens the wood beneath 
the knots was injured considerably but it 
was through the action of some insects 
which had found a convenient lodgement 
in the knots. In the interior of the knots 
there were cavities of greater or less size 
which were also the work of insects. Ex- 
amining the loose, spongy tissue with a 
compou n d 
it was 
made up of 
and very 
f o r m e d 
through 
scatte red, 
thickly 
quite spar- 
si e n d e r 
the mycel- 
fungus which had caused 
growth. This mycelium was 
microscope 
found to be 
enla r g e d, 
irregularl y 
woody cells 
which were 
sometim e s 
sometim e s 
ingly, the 
threads of 
ium of the 
the distorted 
clear and 
colorless excepting near the surface where 
it rapidly became dark brown and finally 
black, forming over the knots a dense, black, 
crust-like covering. The formation of the 
knots appeared to be entirely due to the 
action of the fungus on the cells of the 
cambium — these having been excited into 
a very rapid and irregular growth. 
Inour vertical section through one of the 
knots we notice, if we look sharp, that 
where the cut passes through the little 
pimples above referred to, and we can 
make no cut without bisecting a number of 
them, each of these appears to be filled 
with some white substance. (In the older 
knots they present only an empty cavity 
in the center. ) A section cutting through 
three of these pimples is illustrated enlarged 
in figure 1591. Placing a bit of this white 
substance under the microscrope its nature 
is clearly brought into view and we see, as 
we have already said, that the little pimp- 
les are the fruits of the fungus. They are 
called perithecia and lining the cavity of 
each is a delicate tissue composed of small 
transparent cells; growing from this and 
directed towards the center are a great 
number of 
club- shaped 
ruptly nar- 
the base or 
point of 
These are 
p a r e n t 
which the 
formed, the 
the latter in 
being eight, 
with these 
elo n g a t e d 
bodies, ab- 
rowed a t 
near their 
attachment . 
simply trans- 
sacks within 
spores are 
number o f 
each sack 
M i n g 1 e d 
spore - c o n- 
Flg. 1569. 
taining sacks are many long and slender 
thread-like growths that are slightly enlar- 
ged at their tips. Figure 1590 is reproduced 
from a drawing, very much enlarged (the 
scale to the left shows the magnification, 
10M-1-2500 of an inch), of these spore sacks 
with tbeir intermingled threads, taken 
from one of the perithecia shown in section 
in figure 1591. Within the sacks the spores 
are clearly visible. The latter, shown sep- 
arately in figure 1592 where two of them 
are seen to be germinating, are elongated 
oval in shape, broadest above. Near the 
narrow end is a transverse wall or septum 
which d i- vides the 
spore into £ o two very 
unequal cells. _ KA ['--y' The smaller 
of the two /S) cells is much 
thinner wall- | | ed than the 
otli e r a n d ^ njjsn appears to be 
rather an \ ml/ appendage 
to the spore than a P art 
of the spore itself. 
Such are Fig. 1588. the charac- 
teristics, briefly told, which were exhibited 
by the specimens of black knot received 
from New Jersey, or which can be seen in 
any of the knots in April or very 
early May. Just at what season the 
spore-sacks and spores which we have 
described and which belong to the ma- 
ture state of the fungus, are formed, we 
cannot positively say, but it is probably dur- 
ing the later winter months, or in those of 
early Spring. At this season (the first of 
May) they are evidently ripe and ready to 
reproduce the fungus whenever they shall 
escape from their sacks and find a proper 
lodgment on the bark of some plum or 
cherry tree. That they do germinate upon 
the bark and by some means gain access to 
