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 Bad. 

 tumejacicns 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 19 10 my results on these 

 plants were inconclusive, owing to loss of virulence on the part of the cultures used. So 



far in 191 1 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 

 on plants freely and repeatedly inoculated, 

 but it may have been only lessened virulence 

 of the organism used. The plants are still 

 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, i. c, 105 plants inoculated in 208 

 places with the formation of 20S 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, /. c, 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, i. e., 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. 



Fig. 30.* 



1898. Shattock. Samuel G. The healing of incisions 

 in vegetable tissues. Journal of Path, and 

 Bact., Edinburgh and London, 1898, vol. V, 

 pp. 39-58, 2 pi., 6 text figs, 



1903. Hiltner, L., und Stormer, K. Neue Untcr- 

 suchungen iiber die WurzelkuoUchen derLegu- 

 minosen und deren Erreger Arb. a. d. 

 Biologischcn Abt. fiir Land-und Forstwirt- 

 schaft am Kaiser. Gesundheitsamte, 1903, 

 Bd. Ill, Heft 3, p. 151. 



1907. BRiiLLOWA, J. p. Ueber den Selbstschutz der 

 Pflanzenzelle gegen Pilzinfcktion. Jahrb. f. 

 Pflz. Krkh., K. Bot. Garten Petcrsb., 1907, 

 Nr. 4. 



1910. AlTEn, H. von. Zur Th}dlcnfrage. Callus- 

 artige Wucherungcn in vcrlezten Blattsticlcn 

 von Nuphar lutcuniSm. Bot. Ztg., 1910, Part 

 II, vol. 68,89-95. 



*FlG. 30. — Cross-section of woody part of a young mulberry .shoot (3 months old and growing rapidly) showing 

 injuries due to BacL 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 inoculation and 30 cm. 

 below any external appearance of disease. The only vessels showing tyloses arc those affected by the bacteria. Inocu- 

 lated near ape.x of shoot on Feb. 11 1909. Drawn from an unstained free-hand section Mar. 15, 1909. Zeiss 8 mm. 

 obj., and No. 12 ocular 



