344 
Essed — The Panama Disease . /. 
the older leaves show signs of decay, whilst the buds develop for a certain 
length of time, depending of course on the direction followed by the germ 
in propagating through the rhizome : this may be called the first stage. 
In the second stage development stops, the leaves droop, the plant looks 
water-starved, wrinkles appear on sheath and midrib of the leaves, which 
gradually dry up, and finally the pseudo-stem bends down along a line 
of least resistance. 
As soon as the disease becomes evident, one is sure to find the 
tuberous rhizome, when cut asunder, showing on the exposed surfaces more 
or less signs of putrefaction. The healthy whitish colour is replaced by 
a yellowish hue with reddish brown spots or streaks scattered through the 
infested parts, and yellowish or brownish mucilage exuding from the slime 
canals. The roots do not participate in the process of decay before the 
tissue at their base is affected, proving that the germ does not enter 
by them, and since the starting-point of disintegration could be traced 
to an old wound-surface there is reason to assume that the fungus at 
the start behaves as a wound parasite or saprophyte, living at first on the 
exudation and by degrees preparing its way up into the damaged vessels. 
Sections made from the rhizome showed at once that a fungus was the 
probable causa morbi. The mycelium is mainly massed in the wood vessels 
and the immediately surrounding tissue (see PI. XXVIII, Fig. i). The water- 
starved appearance of the affected plant is readily explained by the enor- 
mous amount of hyphae and spores in the vessels, which must seriously 
interfere with the passage of water. But a more effective impediment to 
the transpiration current and assimilation in general are the at first mucila- 
ginous bodies plugging the wood vessels and sieve tubes and filling up cells 
and intercellular spaces of the parenchyma. These cartilaginous bodies 
I shall henceforth term sclerotia , 1 which I shall prove them to be. 
The damage done by the fungus is not only of a mechanical but mainly 
of a physiological nature, as may be concluded from the wood vessels being 
discoloured and the contents of the sieve tubes, &c., resorbed by the hyphae 
running through them. The changes in the parenchyma seem at first to be 
slight, and manifest themselves by an unusual turbidity of the protoplasm, 
apparently caused by the action of an enzyme secreted by the fungus, 
to which enzyme also the brown discoloration and slimy degeneration of 
the cell-walls may be due. By degrees the contents of the cells are 
absorbed and replaced by the cartilaginous sclerotia. Some details of the 
formation of the resting mycelia may be mentioned here ; on hyphae 
passing from cell to cell comparatively large, bladder-like structures arise, 
which, sometimes wrinkled and lobed, then again split in tufts and 
divided, seem to exercise a haustorial function. The enzyme alluded to 
before is probably secreted by these structures, as may be inferred from the 
1 Another name for these structures is perhaps desirable. 
