58 QUEENSLAND AGRICULTURAL JOURNAL. [1 Juny, 1899. 
a pallid hue, and the tissue immediately beneath is quite soft and translucent, 
and has a fotid odour. The larger areas become superficially discoloured, 
though the line separating these from the still unaffected parts is not yet very 
pronounced. As the underlying tissue softens, the skin covering these areas 
readily collapses on pressure ; scattered over its surface are white pinple-like 
elevations—marking the site of the lenticels or breathing-pores; rents appear in 
it, and from the ruptured surface emanate masses of a creamy pus-like 
tenacious substance. The whole potato is now most offensively odorous ; but 
the pungent sour smell which arises from ordinary rotting potatoes is not 
noticeable. Exposed to the air, the tuber soon becomes, after blackening, a 
‘mere mass of corruption’; in the soil—as in a damp chamber—it is transformed 
into a receptacle filled with a white slimy fluid, that, when the diseased plant is 
raised, streams out. E 
If tubers in which the initial stage in the progress of the disease is past 
are cut across, it will be found that the softening of the tissue commences here 
and there just beneath the surface, and between it and the ‘ ring,’ and con- 
tinues to develop in this position until two-thirds of the superficial tissue is 
completely broken down, and may, in fact, be removed by washing; leaving the 
central portion still solid, not even as yet discoloured, and with irregular’ 
bounding surfaces as if it had been gnawn into. The cut surface on exposure 
to the air commences almost immediately to assume a light-brown rust-like 
colour, especially along the course of a band separating the portion of the 
tissue that is still intact from that which is already disorganised. ‘This alteration 
soon, however, becomes general, the solid tissue being the last to participate in 
the change, excepting only the centre itself. It, too, gradually becomes of a 
more and more intense hue, until almost the whole surface is ultimately dull 
black. Step by step the solid tissue participates in the softening and decay 
encroaching inwards from without. 
The time that is oecupied in these destructive changes is greatly influenced 
by meteorological conditions. When warmth and moisture preree it is a mere: 
question of hours, so that not infrequently, even when the haulm is still quite: 
een, the tubers themselves may be found to have already completely broken. 
own. How rapid is this decay in its progress is illustrated in the followin 
incident :—A_ selector at Ravensbourne, whilst unearthing a diseased crop, 
which had been affected at a late stage in the growth of the potato, picked out 
some mature tubers which were exceptional for their size ai apparent sound- 
ness. Placing these in a shallow excavation in the soil, he Neves them almost 
immediately with earth, but on exposing them a few days later, in the presence 
of the writer, many in consequence of the disease, whose occurrence was in 
their case previously overlooked, were already in a semi-fluid putrescent con- 
dition. With regard to the tissue of the stem, this gradually decays from the 
base upwards, the central pith, which is perhaps the first part of it to be visibly 
affected, being early abnormally moist and light-coloured.* 
Though occasionally an entire crop may be smitten within 2 or 8 weeks, 
the disease does not, as a rule, at once affect it to the full extent of its subse- 
quent distribution, but for days after its first manifestation continues to spread 
through the cultivation, by the intervals between affected plants or groups of 
plants being obliterated or bridged over by fresh outbreaks. . . . . Isolated 
plants along a row may alone be subjected to it, and, perhaps, only partially go,. 
or it may affect patches of varying size and configuration ; though neither the 
form nor the extent of these diseased areas seems to be in any way related to any 
special contour of the land or to any local variation in its texture or other 
physical feature. : 
All varieties of potatoes growing in the districts in which the disease occurs 
seem to be liable to its attacks, amongst them being Harly Rose, Brownell’s 
Beauty, Circular Head, Snowflake, &e. 
* Since this was written it has not infrequently been observed that the wilting of the haulm 
has preceded the occurrence of any decay of the tubers beneath. In such instances there has- 
been reason to infer infection of the plant through insect incculation. 
