Medical Officers of the Army of India.
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oospores which are liable to be present within the tissues of dead and blighted
plants, the latter must serve as a means of securing the recurrence of the blight
from year to year if they be allowed to remain in the soil of any area within
which the cultivation of potatoes is annually conducted. The oospores, being
capable of lying dormant for prolonged periods so long as they are kept dry, will
readily survive in the soil for an indefinite time and retain their capacity for
producing mycelium, primarily of a saprophytic type, but ready to adapt itself
to parasitic existence whenever it meets with a suitable host.
c. A leaf-blight termed " Farrah" by the natives of Oudh. —This is a form
of blight which differs from the previous one in primarily affecting the leaves
and tips of the stems of the host, and has of late years occasioned considerable
mischief among crops in the neighbourhood of Lucknow. Specimens of
plants affected by it were sent to me by Mr. Ridley, the Superintendent of
the Horticultural Garden, Lucknow, in March 1893. They showed no traces of
the presence of Phytophthora, but the tissue of the leaves was everywhere
permeated by mycelium, whilst the surface was covered by a crop of emergent
fructifying filaments of two distinct forms. One, and by far the most abundant
of these, consisted of erect, unbranched filaments capped by clusters of large,
colourless, uniseptate, obovate conidial bodies which germinated freely in water
(Plate I, Fig. 16). The phenomena attending germination were somewhat
peculiar in character, for the conidial cells only germinated directly in a com
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paratively limited number of instances, whilst in most cases a considerable
increase in the size of the cells occurred, and at the same time the contents
became clothed with a special cell-wall. The walls of the parent cells then
gradually disappeared and the original bilocular conidia came thus to be
replaced by pairs of cells, which generally remained associated in couples, but
sometimes became completely isolated from one another ; and it was not until
these preliminary processes had been completed that germination occurred. It
appeared in fact as if each of the loculi of the original conidioid bodies became
converted into a unisporic sporangium ere germination took place.
The second form of fructification which was present, presented the
characters of Fusisporium Solani, Mart., occurring in the form of slender branched
filaments, which were frequently arranged in the form of dense tufts, bearing
slender, septate, curved, fusiform conidia (Plate I, Fig. 16). There can be no
question that the mycelium giving origin to this form of fructification cannot
reasonably be regarded as the cause of the blight, but had been saprophytically
developed within the already dead tissues, and this may have been the case with
the other form also. It remains, however, also possible that it may have been
the original cause of the disease. It was naturally impossible definitely to settle
this question in Calcutta, where potatoes are not cultivated, and where the
specimens only arrived after they had been exposed to a journey of several