20 PART 1V.
Microscopic EXAMINATION OF DisEasEp NuTs.
The lesions which are very conspicuous in the older nuts, can first
be detected as faint, pale, waterlogged areas on the green husk and if
the nuts are cut open, as faint discolourations scattered in the interior
of the husk; they originate internally and are due to the gradual
breaking down of the cells, a process which continues till the exterior
is reached. The first indication of a lesion isthe swelling of the
middle layer of the cell wall and. the pushing apart of the cells, which
have the appearance of being perfectly normal and healthy. A search
failed to reveal the presence in or near the lesions of either intracellular
 or intercellular fungi or bacteria which might, by the secretion
of enzymes as with Botrytis, cause a disintegration of the cell wall.
No fungi were found in the tissues of the husk near the lesions or in
the peduncle. At a later stage the cells of the husk disintegrate and
a semi-liquid substance is found in the resulting cavities; when the
lesion reaches the surface, one of two things happens, either the liquid
does not exude and the exposed fibres dry or the exudation is copious
and the liquid dries in the form of hard drops or lumps. There is
some evidence that this formation of hard gum is due to a fermentation
which occurs in the exuding cell sap in the air owing to the presence
of various secondary fungi. A similar formation of gum can be
induced artificially if the petiole is cut so as to cause an overflow of
sap.
Funa1 as CAUSE oF DISEASE.
As is to be expected the older nuts with dry husks often have a
conspicuous growth of fungi, chiefly Diplodia .epicoccus and a
Glaeosporium but these are not always present on diseased nuts and
indeed are more often found on healthy nuts. Suspensions of the
spores of the various fungi found were sprayed on the flowers and
young nuts of trees bearing healthy inflorescences but in no case was
disease induced and no evidence was obtained that they are the cause
of the disease.
A study of the peduncle failed to produce any evidence of
abnormality in the tissues or any signs of mechanical injury which
might check the flow of sap below the inflorescences.
The stems except for past injury due to beetle attack were normal
and showed no injury due to fungi. Ip a few cases on the margin of
the cracks in the stem which are due to rapid growth, small colonies
of a Spheronema were found and in two other cases a Thielaviopsis,
probably T. paradoza. Microtome sections were made of the
surrounding tissue but no marked fungal penetration was found and
it was concluded that the fungi were growing on the sap exuded from
the cracks in the stem.
Sections of the root failed to show any abnormal condition of the
tissues, neither fungi, eelworms nor insect pests have been found.
NoN-FERTILISATION AS CAUSE OF THE DISEASE.
Many mature trees produce inflorescences with female flowers
which never swell but fall off without developing. When these flowers
were examined and compared with the flowers of a healthy
inflorescence it was found that the abortion was due to lack of
fertilisation; pollination had occured, the pollen had germinated
though the tubes were poor but they had not been able to grow down
the micropyle as the micropylar canal was closed. In the normal

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