THE NATIONAL NUliSEKYMAN 
:]18 
may act. as a serious centre of infection to plants such as Rasp- 
l)erries and Loganberries which may be subsequently planted. 
From the point of view of inspection of stocks, it is quite an 
easy matter to remove galls from slightly affected stocks, and 
smear the newly made wounds with earth so as to evade de¬ 
tection. 
In such cases only a careful miscroscopic and biological ex¬ 
amination can disclose the presence of freedom from the disease. 
With regard to the susceptibility of Apple stocks, it has been 
noted at East Mailing that the different sorts of paradise differ 
markedly. 
The most susceptible are certain types which root rather 
poorly when layered, and which, consequently, have to be torn 
or broken from the stool. 
No kind of Apple stock has yet been found to be immune, and 
traces of the disease have been shen on several kinds of free 
stock which have been propagated by layers as well as on the 
common forms of paradise. 
The work carried out on paradise stocks, known to be suscep¬ 
tible to Crown Cxall, showed that the galls occurring on the base 
of the stocks were distinctly larger where the stocks have been 
roughly torn from the stool than where smoothly cut with a 
knife. 
Covering the wound before planting, with Stockholm Tar or 
grafting wax, especially the former , reduced the number and 
size of the galls, but also appeared to injure the roots to some 
extent. Probably this was due to the poor rooting of the stocks. 
The latter, planted with their bark bruised severely, showed 
after two years’ growth a considerable proportion with galls on 
the main stem above the base, whilst uninjured stocks were 
practically free. Many of the cut roots bore small galls at the 
cut ends. 
This disease has also been reported on Beets in Denmark. 
In South Africa, Crown Gall was first recorded by Sounsbury, 
in 1910, the disease had then only been observed in the North 
Eastern districts of the Cape Province. It is known to exist in 
all parts of the Union, being especially prevalent in districts 
liable to hailstorms. It frequently occurs on Willows, and is 
probably widely disseminated by the planting of diseased 
cuttings. 
The disease may manifest itself in two forms, known respec¬ 
tively as Crown Gall and Hairy-root. It has been estimated that 
in the nursery 90 per cent, of the galls appear on the scion just 
above the point of union with the root. 
Young galls are comparatively small greenish or nearly white, 
fairly smooth, and soft or spongy in texture. 
When matured they are usually hard and dark in color, and 
from one to several inches in diameter. The disease spreads 
very rapidly, over 2,000 trees having been infected in 1912 from 
a single infection on a Willow in 1907, 
Hairy-root occurs on Apples, and is quite different from the 
form described above. 
There is an extensive production of small fibrous roots grow¬ 
ing out at right angles singly or in tufts from an older root or 
stem. There may be a broomlike formation with extensive 
branching of the roots at the ends, or the disease may take the 
form of a wooly outgrowth originating from a smooth irregular 
swelling on the larger roots. 
The disease has also been reported in isolated cases on the 
Paris Daisy (Chrysanthemum frutescens). Rubber plant (ficus 
elestica), Bryophyllum, Pear Lucerne, Tobacco, Pear, Quince, 
Plum, Cherry, Apricot, Peach, Raspberry, Loganberry, Black¬ 
berry, Hollyhock, Beet, Mangold and Roses in America. Vines 
in France and Italy. 
In a crif.cal study of Crown Gall carried out by Robinson and 
Walkden (University of Manchester), 192.3, a new light has been 
thrown upon the occurrence and distribution of the bacteria 
which cause this disease. 
The investigator has been concerned with Crown Gall on 
Chrysanthemum frutescens and Nicotiana affinis. The work has 
included the artificial production of primary galls on the Chry¬ 
santhemums from the earliest stages, the distribution of the 
casual organisms in the galls, and the development of the sec¬ 
ondary tumours and tumour strands. 
A different interpretation has been given to experimental re¬ 
sults similarly obtained by Smith in his work. 
The investigation shows, that in the inoculation experiments 
galls were formed, and on those exhibiting a rough surface large 
numbers of the bacteria B, tumefaciens were found. These in 
part, at any rate, are considered responsible for the shape of 
the gall which results from the localisation of the disturbing 
influence in definite regions of the stem. 
It must be pointed out, however, that in the Chrysanthemum, 
the organisms are not found at any considerable distance from 
the surface, and soon the form of the growing gall becomes such 
that the majority of the organisms producing it are localised 
on its surface. 
Whilst dealing with the inoculations of the plant (Chrysanthe¬ 
mum), it is pointed out that on several occasions auxiliary shoots 
were inoculated which were growing from positions very near to 
galls produced by earlier inoculations. Galls on such shoots 
were invariably obtained showing that there is no immunity 
acquired by plants against Bacillus tumefaciens following an 
earlier infection by the Crown Gall organism as has been pre¬ 
viously suggested. 
The air-loving character of this organism may account for the 
fact that the bacteria vdiich are introduced to the interior, either 
of vessels or intercellular spaces, do not multiply to any extent 
nor grow progressively in the interior. 
The investigators next proceeded to test the view suggested 
by W. H. Lang, viz., that the appearance of the secondary galls 
and of tumour strands was due to the subsequent development, 
growth and extension of the formative plant tissue under the 
influence of the bacteria after inoculation. 
The results have shown that the secondary galls on the leaves 
of Chrysanthemum frutescens are largely accounted for by the 
bacteria inoculated into the young primary woody plant tissue 
being carried by the stretching growth of this to some distance 
from the point of inoculation; the results with Tobacco have 
shown that an actual migration of the bacteria is also possible 
in this tissue. 
Numerous needle prick inoculations of the apices of young 
flowering shoots of this species of Tobacco (N. affinis) were 
made, and results similar to those described by Smith were ob¬ 
tained, but whenever the galls have a rough exterior the organ¬ 
isms are present in abundance on this surface, and when com¬ 
pletely smooth galls occur they, like the secondary galls, have 
the organisms present in the inter-cellular spaces and vessels 
within. 
In the Tobacco, as Smith has shown, these frequently burst 
out to the exterior, either from the pith or the cortex, and the 
rough surface which they then acquire is richly populated with 
the Crown Gall organisms. 
The authors have obtained no evidence of the migration of the 
strands of tumour tissue to any distance at all comparable with 
that postulated by Smith, but they have clearly shown that the 
effect of the bacterial influence and stimulus proceeding from 
definite centres invariably results in the sub division and en- 
enlargement of the cells. 
The presence of the causal organisms of Crown Gall oir the 
exterior of the galls explains the extreme ease with which the 
soil in which diseased plants are grown becomes highly infect¬ 
ious, since the organisms must be washed into the soil during 
watering operations or whenever rain falls on the plants. 
It has also been observed that the most striking growths of 
Crown Gall are always obtained when regions of the plant which 
are capable of making considerable further growth are in¬ 
oculated. 
Control Measures. 
In the case of Manetti Roses, which are particularly liable to 
infection, it is very desirable to propagate such plants in only 
“known as clean soil.” 
All soil infected with the Crown Gall organism should be rigid¬ 
ly avoided, and, of course, infected stocks should not be planted 
into clean soil. 
Sterilization might be advantageous on a small scale, but its 
application under commercial conditions is a practical impos¬ 
sibility. 
Great care should be exercised when handling stocks during 
the routine of propagation, etc., in preventing the production of 
wounds, when shifting, healing-in, etc. 
In the operation of grafting, care should be exercised in select¬ 
ing stocks of suitable size, and to well wrap and cover the graft. 
The latter is most important where the graft is in close prox¬ 
imity to or just below the soil level. 
The removal of galls does not mean removal of infection. 
Badly galled trees should be grubbed and burnt. 
L. 
