Medical Officers ofthe Army of India.
109
of the blight of Ficus stipulata, but of considerably larger size than these ever
are (Plate II, Fig. 1). The affected tubers showed little conspicuous evidence
of disease externally, but were more or less softened in texture, and, on being
laid open, were found to contain irregular cavities of greater or less extent, the
walls of which were coated with thick fleeces of white mycelium. On removing
these the subjacent tissue was found to be softened and pulpy for some depth,
but appeared not to be penetrated by any fungal elements. In spite of this,
however, both the growth of mycelium and the softening of tissue continued to
advance rapidly in a moist atmosphere until the tubers were reduced to mere
shells containing masses of fungal elements and a moist, ill-odoured pulp. When
the nutritive supplies afforded by the latter were exhausted, the sclerotia
produced large numbers of sclerotia of ovoid form with average diameters of
75 X 52 µ, originally pure-white or pale ochreous throughout, but ultimately
assuming a deep, rich brown tint externally (Plate II, Fig. 1).
Numerous experiments were tried in regard to the infective power of the
mycelium, and it was ascertained that it was capable of giving rise to spreading
blight when applied to the leaves of Ficus stipulata and various kinds of
Begonias, the filaments rapidly extending over the surfaces and at the same
time invading the interior by penetrating the stomatic orifices. When applied
to the outer surfaces of intact potatoes, a considerable amount of growth
occurred in moist atmospheres, but no penetration of the tissues occurred, and
the spread of the mycelium was soon arrested without having caused any
damage. The effects were, however, very different when the continuity of the
rind was interrupted at any point reached by the mycelium, or when the latter
was applied direct to raw surfaces. Under such circumstances luxuriant and
continued growth occurred, fleeces of white filaments accumulated, the subjacent
tissues softened, and, as time went on, all the phenomena present in the case of
the original diseased tubers were repeated. In this incapacity for affecting
intact tubers and rapid destruction of those presenting raw surfaces, this blight
resembles that occurring normally on the leaves of Ficus stipulata, and differs
from that obtained from Evolvulus nummularia, which, although incapable of
penetrating the general surface of the rind, does attain access to the interior of the
tubers by means of the tissues of the eyes, especially when the latter have under
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gone a certain amount of development and have come to present somatic orifices.
The occurrence of extensive destruction of tubers by this form of blight
thus implies the presence of some adjuvant agency facilitating access by
establishing breaches in the continuity of the epidermal surface. Such solutions
of continuity may of course arise in many different ways, but in the instance
of this particular sample of tubers there could be no doubt whatever what
the really effective agent was, as the tubers were not only affected by the
mycelium but also by a species of Acarus ; the tissue beneath the fleeces of