Medical Officers of the Army of India.
35
thus arisen are zoospores. They soon begin to show, movements and the cell
becomes occupied with a dense mass of swarming bodies. Rupture of the cell-
wall now occurs and the zoospores emerge in rapid succession and swim off
actively in the surrounding fluid. The process of emergence does not seem
to be limited to any special period, or, at all events, the period is an extended
one, as emergence has been observed to occur from early in the forenoon to late
in the afternoon.
The zoospores are biflagellate, and on emergence are pear-shaped with the
broader portion of the body bright green and the narrow anterior flagellate area
colourless (Plate III, fig . 9). It is of course difficult to obtain accurate
measurements of such active bodies, but, so far as could be ascertained, they
measure about 7 to 8 µ in length and about 5 µ in breadth. They swim about
very actively with a combined movement of rotation and progression. The body
contains several large, refractive particles, probably of amyloid nature. Large
numbers of them conjugate to form zygozoospores (Plate III, fig . II ). In
this process two of the zoospores approach one another closely, their anterior
pointed extremities come into contact and a gradual process of fusion spreads
backwards along the bodies until complete union has been effected. In ex-
ceptional cases three, in place of two, zoospores unite in this fashion. The
normal zygozoospores are, of course, considerably larger than the zoospores,
and are generally more or less spherical, even from the outset. They are
provided with four flagella and continue to move actively about for some time.
The movements, however, soon decrease in energy, the body ceases to progress
freely through the water; it settles down and after keeping up a tremulous move-
ment for some time becomes quite motionless. Parallel phenomena of change of
form and cessation of movement occur in those zoospores which do not conjugate.
All the zoospores developed in a zoosporangium do not always effect an exit,
but a certain number remain behind, and after swarming actively for some time
gradually become spherical and motionless (Plate III, fig. 10). Such motion-
less, retained zoospores measure about 7 µ in diameter. After settling down
apart from leaves of Limnanthemum or on the general surface of the leaves the
zoospores show no further developmental change. They never germinate like
those of Chlorochytrium and soon lose their green colour and disintegrate. The
actual process of invasion of new portions of leaves has never been observed, but
from the appearances present in various cases there can be no doubt that
the zygospores and probably zoospores also gain access to their sites of further
development by direct transit through the stomatic orifices. In many cases the
latter can be seen to be as it were plugged by bodies which have failed to
secure entrance, while in others circular bodies, identical in characters with
the still zygozoospores and zoospores, can be detected in the substomatic spaces.
From the dense aggregation of large groups of zoosporangia which .so frequently
occurs it would appear that, as a rule, the zoospores do not travel far, as it
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