Medical Officers of the Army of India.
113
numberless emergent fructifying filaments which force their way outwards to the
surface (Plate III, Fig. 3), At the same time, they in their turn give off de
-
scending processes (Plate III, Fig. 2), like those from which they originated,
which force their way downwards into deeper portions of the cortex and give
rise to new horizontal expansions. During periods of sunny weather and rela
-
tively low atmospheric humidity, the active growth of the algal elements will
naturally be retarded, and, at the same time, the superficial layers of them and
the disintegrated cortical tissues will tend to dry up and become detached,
whilst the deeper strata of the host-tissues, which retain more continuity, persist
and afford protection to the algal elements which they contain. When, on the
other hand, conditions of excessive humidity once more prevail, active growth
will recur and provide for additional disintegration of the host-tissues, and these
processes being recurrently carried on, complete destruction of the cortex will
ultimately ensue, and the entophytic elements no longer meeting with a suitable
nidus, will also disappear, leaving the bast-tissue completely denuded.
The mere abnormal drain upon the water-supply of the host incident on the
demands of the intrusive algal elements must necessarily tend to interfere with
the nutrition of all distally situated parts even from the outset, and, with the
advance towards complete decortication, a purely physical evaporative drain
must be established, the ultimate result of which will be a fatal defect in distal
water-supply.
The disease is described as tending to occur specially in particularly damp
sites, which is just what might have been expected from its origin, seeing that
excessive damp must on the one hand favour the vegetative growth, and on the
other the reproductive diffusion, of the alga. At the same time the destructive
effects which it produces are likely to occur most rapidly and conspicuously in
sites which are freely exposed to the sun, and therefore at particular times of year
subject to considerable desiccation, as this must both facilitate decortication and
also render any abnormal drain on the water-supply of the host more injurious.
Under the influence of excessive moisture, on the other hand, the extension of the
Entophyte within the host-tissues will occur rapidly, and fructifying filaments will
appear in abundance on the surface of the diseased areas and produce innumer
-
able sporangia, the zoosporic contents of which only require the presence of
abundant moisture to become fully developed and endowed with active move
-
ment securing their diffusion. They will thus be able to spread from their
site of development to other previously unaffected areas, and, on germinating,
to serve as sources of infection there. Their diffusion, moreover, under the
influence of excessive moisture will tend to be effected not only actively, but
passively, as multitudes of them may readily be conveyed in any drop of water
running along a continuous surface, or falling from a higher to a lower one.
There is unequivocal evidence of this in the excessive prevalence of Cephaleuros,
Q