Vermont phÅ“nix. [volume] (Brattleboro, Vt.) 1834-1955, 1889-08-09

FOR a long time the cause OF this disease /
was imperfectly understood, and it was as
cribed to different causes by different scien-
fists. 1t is now pretty well settled that it |
is caused 10y parasitic fungus, the species |
of which are well identified and its nature
understood The scientific name of the !
fungus which causes the potato rot is Per
onosapora iniestaus. or another name used
10y later writers for the same thing is Ply
tophthora infestans Mr. Erwin F Smith
an expert microscopic who has made a
study of fungi, says that the brown or black
discoloration Of the tubers and the blight
of the leaves have been thought by many
of the growers to be different diseases, but
they are only two phases of one disease,
being due to the same fungus During the
growing season the mycelium of this species
may he found in the diseased stems and
leaves. and if there be sufficient moisture
in the air, the summer spores are produced
by myriads upon tie diseased vines These
spores blown about by the wind or carried
10y insects, birds or other animals, find lodg
ment on healthy plants Dry air soon de
stroys them, but in drops of dew or rain
they terminate freely, so that many thou
sand new centres of infection may begin in
course Of a single day. The sudden rot of
the green tissues of the plant so often oh
served when the weather is warm and wet
is due to the rapid propagation of the plant
10y means of these summer spores, although
the direct breaking down of the tissues is
generally caused by bacteria, or by another
species of fungi
Farmers generally believe that the disease
spreads downward from the stalks To the
potatoes, and that the progress of the rot
may be arrested or retarded by early dig
ging. 1t is "A question: however, whether
they are not less exposed to the contagion
in the ground than when dug and stored in
the cellar III hot weather. We have allow
ed potatoes to remain in the ground till late
III the season without discovering any in
crease'of rot in the tubers after the vines
were killed by the disease, while others
that were dug early in August rotted bad
ly in the cellar. On this point we refer
again To our expert, retaining for the want
of any accurate substitute, his use of tech
meal terms. Mr.. Smith says that undoubt-
eddy the myceium of PMotphhord may
grow down through the stalks and thus
reach the tubers but this has never been
proved The tubers are ordinarily infect
ed by the conidia, which may be washed
into the soil by rains or carried down by
small animals. A wet rot of the tubers
does not always follow their infection
Very often the only indications of disease
are some superficial discolorations of the
tubers These brown or black spots con
tain the mycelium of the fungus At first
these spots are scattering and mar the sur
face of the tuber, but during the winter
they may increase in number and size as
the mycelial threads penetrate farther and
farther into the sound tissue 81 have
found the minute threads of this fungus
penetrating the sound tissues for some dis
lance lone centimeter or morel beyond the
discolored parts of the tuber, and, by ex-
posing these white and apparently sound
portions to moist air for some DAYS, have
obtained conidiophores and conidia with
which have caused the rot in other pota-
toes previously sound This is, however
no new experiment others have obtained
the same results. That in damp warm
cellars or pits the summer spores may be
developed on the surface of infected tn
hers, and that the neighboring sound ones
may thus be infested. is no longer matter
of speculation, but has been settled in the
affirmative by observation.
This fungus is supposed TO live from year
TO year 10y means of its myceium lodged
III the tuber. The mycelium corresponds
somewhat 10 both the roots and stems of
some of the higher kinds of vegetable
growths These develop the summer spores
from which the contagion is spread, and
possibly under favorable conditions winter
spores may survive. The parasite finds its
way 10 the field along with the planted po-
tatoes, either concealed as mycelium with
in their TISSUES or adherng 10 the surface
IN the form of recently developed conidia
lsummer spores accidentally lodged there
ON. The mycelium may grow from the tu-
Der in the shoots, reach the surface and
fructify in this way, or it may develop the
summer spores in the soil upon the surface
of the tuber whence they may find their
way To the leaves and stems by aid of in
scots
In favorable weather the propagation
of the fungus by summer spores is so rap
id that only few original centres of infec
ton are requisite in order 20 speedily in.
fest "a whole field or district Certain con
ditinns iavoring rot are beyond control of
the farmer. He cannot prevent warm,
wet weather but by planting upon dry
ground aud using the greatest care in the
selection of tuhers for planting, he may
greatly diminish the severity of the dis
ease No tubers having dark spots or
blotche- on their surface, or which look
black in places when cut open, should be
planted Whether early or late sorts will
r1t worse depends upon the character of
the SEASON. neither the rainy season Is
early ~ late. other things being equal