Medical Officers of the Army of India.
25
mm. In form the spores are obovate. They are of a rich, golden-brown
colour over the greater part of the surface, and deep brown over the apex, due to
the increased thickness of the epispore here (Fig. 9, Plate I). Over the upper
half of the spore the epispore is thickly tuberculate, and below this scattered
tubercules are also present. About half-way up a series of circular pores form a
band around the body of the spores (Fig. 8 a , Plate I). Each spore contains a
large, pale nucleus, surrounded by a mass of cytoplasm, which, in the case of
the first crop, is often more or less coarse and lumpy in texture, but in that of
the second one is finely granular.
When an infected leaf fades, the tissue in, and immediately around, the pus
-tular patches retains its brilliant green colour long after the rest of the surface
has become bright yellow, and the same phenomenon holds good in regard to
teleutosporic patches. This indicates the fact, which is borne out by micro
-scopic examination of sections, that there is no injury to the vitality of the
tissue-elements of the host within the specially infected areas. On the con
-trary, there is very manifest evidence of protoplasmic hypertrophy, especially
in the epidermal cells, and the parasitic and host elements appear to hold a
relation to one another very similar to that which the fungal and algal elements
hold in many lichen thalli. Within the green pustular areas the chlorophyll
corpuscles are plump and well preserved, and there is manifest excess of colour
-less cytoplasm specially in the epidermal cells. In the surrounding yellow
areas the cytoplasm generally is very scanty, and the chlorophyll corpuscles are
represented by mere shrunken, yellowish granules. It might at first sight
appear that the detachment and destruction of cuticular tissue connected
with the maturation of the pustules must necessarily produce an injurious
effect on the subjacent tissues of the host. This is not the case, however,
due, no doubt, to the fact that the exposed surfaces are everywhere covered
by a dense continuous stratum of small-celled fungal tissue, from which the
spores originate and which replaces the cuticle in protective function. As
will be shown in the case of R. stictica, where such a protective surface layer.
of fungal tissue is absent, desiccation and death of the host tissues within
the pustular areas does eventually take place.
For some time only pustules of the character described above, containing
large uredospores, present themselves, and then others of mixed character begin
to appear. In the first form of mixed pustules which appear the pustules contain,
in addition to the large uredospores,varying numbers of much smaller ones (Fig. 16,
Plate I). In some cases these are present in enormous numbers, but they never
occur alone, being always associated with either uredospores or teleutospores, or
with both. They are of narrow, oval form, measure about 8 X 2 µ, and are almost
colourless, having at utmost a pale, bluish green tinge (Fig. .8 b, Plate I).
They contain a finely granular protoplasm and a distinct, pale nucleus, which
stains deeply with Spiller's purple. They are connected by relatively long