1 Jury, 1899.] QUEENSLAND AGRICULTURAL JOURNAL. 59 
It may become manifest at any period in the life of the potato-plant after 
the latter has once appeared above ground. bude As a rule, however, 
the plants which generally evince the disease are from 5 to 7 weeks old, and its. 
retarded occurrence is restricted to crops usually that have been planted before 
the cold season has passed. 
Neither the onset of the disease nor its degree of virulence appears to be 
influenced by the physical texture of the soil or its chemical constitution. .  .. 
The elevation, aspect, contour, and drainage of the land are likewise without 
influence on its occurrence. 
Again, it is met with, as often as not, in the case of potatoes which are 
being grown on newly broken up ground, or where they have not been preceded 
by any other crop. On the other hand, on soil, precisely similar to that which 
has yielded diseased tubers on the first occasion of its being cultivated, five 
good crops have been raised entirely free from the disease, before the one in 
which it eventually occurred. 
Tt occurs also on land upon which the potato crop exhibiting it has been 
preceded by other crops, such as maize or oats, which have been grown con- 
tinuously for two or more seasons. 
Again, it is also felt notwithstanding different methods have been pursued 
in preparing the ‘seed,’ and the cultural operations in raising the crop haye 
been varied. Under some circumstances it may even be concluded that the: 
more the land is stirred the less is the immunity from its attacks. 
It visits both the winter and summer crop to an almost equal extent.”— 
April, 1894.\* 
When potatoes are grown continuously, crop after crop on the same ground,. 
the extent to which the disease manifests itself generally becomes greater and. 
greater with each successive planting, and thus, from a small beginning, a few 
isolated plants only originally evincing its presence, it may ultimately pervade. 
the entire area devoted to the cultivation of this esculent. 
NATURE AND CAUSE. 
Tt is caused by a minute germ, plant-microbe, or bacterium (too small to be: 
seen by aid of an ordinary microscope), that lives and multiplies in the vessels 
that traverse every part of the plant, even extending to the minutest ramifications 
of these in the roots and leaves. These so-called “ sap-vessels’” or tubes, it 
completely chokes up with a sticky, tenacious, pus-like fluid, that is composed of” 
millions of these tiny forms of life. 
And it is by reason of the vast numerical increase of these germs that the- 
plant becomes, as it were, asphyxiated, whereupon the haulm, after wilting, dies 
and the tuber commences to decay—a process that under ordinary conditions of. 
growth is soon perfected. ; 
The germ or active agent in causing the disease can live and multiply 
outside and quite apart from the potato-plant for a considerable time, and, 
owing to the possession of this faculty on its part, it is possible to artificially 
produce the disease—either directly by infecting the plant or indirectly by 
acting similarly to the soil—at will. There are grounds for concluding, however, 
that it gradually loses its vigour and power of originating the malady (in other: 
* These are the leading characteristics of the disease from the farmer’s point of view; and 
although many of them relate exclusively to the malady, yet for its accurate definition it would! 
be necessary to dwell also upon the precise relation in connection with it of the bacillus to whose 
presence and action it is primarily due, and the characters presented by this organism itself— 
including both its morphological as well as its physiological features, as displayed whilst in asso- 
ciation with its victim, as well as when living in other special media. Such a description, with. 
imperfections in some particulars, was given in the illustrated manuscript report of April, 1894, 
which is here cited, under the lengthy section of it, entitled ‘‘Cause.” But for a full and able 
account from this point of view the reader is, however, referred to Dr. Erwin F. Smith’s 
Technical Bulletin, ‘‘ A Bacterial Disease of the Tomato, Egg Plant, and Irish Potato,” forming - 
Bulletin No. 12 of the Division of Va Physiology and Plant BN sy of the U.S.. 
Department of Agriculture, issued in December, 1896, which, whilst setting forth ‘certain 
suggestions in the way of preventive measures that might be adopted,” was ‘intended mainly 
to put pa record (also) the results of investigations concerning the life-history of the organism. 
causing it. 
