Medical Officers of the Army of India. 129
the germinal tubes to the interior of the host, is apparently immediately devoted
to the local production of beds of fructiferous tissue, no time is lost in the
development of new crops of spores.
All attempts to discover any other form of fructification save this uredinous
one have hitherto entirely failed. In spite of the constancy and excessive abund-
ance with which the uredospores are produced, no traces of any teleutosporic
fructification have appeared on any of the numerous specimens of blighted leaves
which have been examined, and, in spite of repeated and careful search, no satis-
factory evidence of the presence of any intermediate host producing the missing
forms of fructification has been obtained. That such an intermediate host
does exist there can, however, be little doubt, as in the entire absence of any
teleutosporic fructification on the leaves of the Teak, there would appear to be
no other theory by which to account for the constant annual recurrence of the
disease. It is not as though the successive crops of leaves normally overlapped
one another, as they do in the case of certain other trees, such as Bassia
longifolia, which are annually affected by uredinous blights devoid of teleu-
tosporic fructification, for a considerable period always elapses between the fall
of one set of leaves and the appearance of the next one. Moreover, during a
prolonged period in the earlier part of the existence of each successive crop of
leaves, the latter show no traces whatever of being affected, and, when they do
begin to do so, the fructification is from the outset uredinous, which may be taken
to indicate that uredospores are the primary cause of infection.
I have, unfortunately, no information regarding the extent to which the
disease prevails in other localities than the neighbourhood of Calcutta, but it
appears to be not improbable that in drier regions its recurrence and diffusion may
be very considerably checked by the absence of conditions favouring the rapid
germination of the successive crops of uredospores. In the lower Gangetic
delta, however, where atmospheric humidity is constantly relatively high and
where heavy falls of dew normally occur even during the driest periods of the
year, the amount of destruction of leaf-tissue which it annually occasions must
be enormous, and must certainly be well calculated to interfere seriously with
the nutrition of the host-trees. The mycelium, no doubt, appears to be very
localised in its distribution throughout the foliar tissues, but the number of
individual points of infection is enormous. Each individual patch of mycelium
may only be capable of acting as a very limited drain on the nutrition of the
host, but the sum of drain determined by the coincident action of innumerable
patches must be very great indeed. Moreover, the destructive effects on the
leaf-tissues are not determined merely by the amount of direct abnormal drain
on nutritive supply by the parasitic elements, for the latter also mechanically
cause such extensive destruction of epidermis as must inevitably lead to the
death of neighbouring and deeper tissues in consequence of the incident S