94 BACTERIA IN RELATION TO PLANT DISEASES. 
it is rather to be expected that some of the many wonderful interrelations now known to 
exist between the attacking bacterium and the resisting animal body may be found to 
apply also in a lesser degree to plants. 
In 1908 and 1909 the writer and his associates Townsend and Brown obtained some 
evidence going to show that after Paris daisies have been several times inoculated by Bact. 
tumefaciens with the production of tumors subsequent inoculations by cultures of the same 
virulence are without effect even on the young tissues of rapidly growing cuttings. 
Subsequent experiments showed that at least a part of this supposed increased resist- 
ance was due to loss of virulence on the part of the organism. In 1910 my results on these 
plants were inconclusive, owing to loss of virulence on the part of the cultures used. So 
far in 1911 we have not been able to obtain 
cultures from galls occurring on non-resistant 
plants, and with virulent cultures from a gall 
which formed on a resistant plant we have 
obtained galls as easily on the resistant as 
on the non-resistant plants, so that the 
problem is still unsolved. 
The writer thought for a time that he 
had achieved resistance to the olive tubercle 
se on plants freely and repeatedly inoculated, 
Caerleon ese = but it may have been only lessened virulence 
CL ey «= soof_ the organism used. The plants are still 
rz under observation. They developed tubercles 
freely when they were stimulated into more 
rapid growth and inoculated from a fresh 
isolation. In fact none of my inoculations 
on olive have yielded a higher percentage of 
tubercles, 7. e., 105 plants inoculated in 208 
Fig. 30.* places with the formation of 208 groups of 
tubercles where inoculated, and subsequent 
metastasis. The organisms which finally failed on these plants after repeated successful 
inoculations were old stock cultures of Californian and Genoese origin, 7.e., organisms plated 
several years before from olive tubercles obtained from these localities. The cultures which 
succeeded so admirably on the same plants under the new conditions, 7. ¢., increased food 
and water supply, obtained by transplanting from pots to a deep bed, were recent isolations 
from an olive tubercle collected in Portofino, Italy. 
Hiltner maintains that when legumes have been infected with a virulent root-nodule 
organism one can not thereafter obtain infections on these plants with a less virulent 
organism, and this appears to be all that has been established for olive tubercle and the 
crown-galls. 
LITERATURE. 
1898. SHaTrock, SaMUEL G. The healing of incisions 1907. Briitnowa, J. P. Ueber den Selbstschutz der 
in vegetable tissues. Journal of Path. and Pflanzenzelle gegen Pilzinfektion. Jahrb. f. 
Bact., Edinburgh and London, 1898, vol. v, Pfiz. Krkh., K. Bot. Garten Petersb., 1907, 
pp. 39-58, 2 pl., 6 text figs. Nr. 4. 
1903. HILTNER, L., UND STORMER, K. Neue Unter- 
suchungen tiber die Wurzelknéllchen der Legu- 
minosen und deren Erreger Arb. a. d. 1910. ALTEN, H. von. Zur Thyllenfrage. Callus- 
Biologischen Abt. fiir Land-und Forstwirt- artige Wucherungen in verlezten Blattstielen 
schaft am Kaiser. Gesundheitsamte, 1903, von NupharluteumSm. Bot. Ztg., 1910, Part 
Bd. III, Heft 3, p. 151. 11, vol. 68,89-95. 
*Fic. 30.—Cross-section of woody part of a young mulberry shoot (3 months old and growing rapidly) showing 
injuries due to Bact. mori, i. e., vessel-walls stained yellowish brown and occupied by tyloses. Bacteria very abundant 
farther up stem, but comparatively few at this level which is about 35 cm. below the point of inoculationand 30 cm. 
below any external appearance of disease. The only vessels showing tyloses are those affected by the bacteria. Inocu- 
. lated near apex of shoot on Feb. 11. 1909. Drawn from an unstained free-hand section Mar. 15, 1909. Zeiss 8 mm. 
obj., and No. 12 ocular. 
oe — 
