March 11, 1904.] 



SCIENCE. 



4IT 



ones propagated from older trees which 

 have been in a hothouse of the U. S. Depart- 

 ment of Agriculture for many years and 

 which have always been free from this dis- 

 ease. The inoculations were made into 

 young growing tissues (shoots) by needle 

 pricks, using subcultures made from single 

 colonies. In this way, using the right 

 organism, knots have been produced on 

 about fifty plants — in fact, on every one 

 inoculated. The tumors began to appear 

 within a few weeks and were well developed 

 in two months. From these artificially 

 produced knots, pure cultures of the origi- 

 nal organism have been plated out in 

 quantity a number of times, and have also 

 been demonstrated in situ both stained and 

 unstained. Young knots are also now de- 

 veloping on shoots recently inoculated with 

 the organism plated oxit of the artificially 

 induced knots. An equal number of cheek 

 punctures made into the same plants, in 

 shoots of the same age, healed promptly 

 and did not develop any tumors. During 

 the seven months covered by these experi- 

 ments only one accidental infection has 

 occur'-ed. This recently discovered knot 

 appeared on an inoculated shoot about fif- 

 teen inches below the punctures (where a 

 tumor also developed), and the infection 

 appears to have entered through a leaf scar. 

 Old tumori?may contain other bacteria, but 

 these when inoculated do not produce the 

 disease. The experiments fully confirm 

 Savastano's statements respecting the bac- 

 terial origin of this tumor, but the parasite 

 appears to be a white rather than a yellow 

 organism. The knot is an enormous hyper- 

 plasia, the exciting influence of the bacteria 

 extending far beyond their actual pres- 

 ence. Various tissues are involved in the 

 tumor and they are miich changed. A spe- 

 cial paper will be devoted to this feature of 

 the subiect. 



Bacterial Leaf Spot Diseases (illustrated 

 by numerous stereopticon photographs) : 

 Dr. Erwin F. Smith, Department of 

 Agriculture. 



This paper was presented principally ta 

 call renewed attention to the fact that bac- 

 terial infection of plants through the ordi- 

 nary stomata is not at all infrequent. Much 

 remains to be done on these spot diseases, 

 but a careful study of serial sections made 

 through very young stages of spots occur- 

 ring on several different plants show the 

 epideiTQis tinbroken and the enclosed bac- 

 terial masses lying in such relation to the 

 stomata as at once to suggest such infec- 

 tion. No other avenue of infection is open. 

 The plum leaf spot and the angular leaf ^ 

 spot of cotton have been studied within the 

 year, particularly with reference to this 

 mode of infection. In case of the spot dis- 

 ease of the larkspur, pure cultures of the 

 bacterium have been plated out of the spots 

 and the disease reproduced in blue hybrid 

 Delphiniums and also in D. ajacis within a 

 few weeks' time by simply putting pure 

 cultures into sterile water and spraying 

 this on the plants. The result of this dis- 

 ease is numerous sunken black spots on 

 leaves and stems, with moi-e or less distor- 

 tion. The inoculations were made in 

 Washington, some in the hothouse, others 

 in a garden. The disease is known to occur 

 naturally only in Massachusetts. The 

 organism is motile, gray-white, nitrate-re- 

 ducing, non-liquefying, and on agar in 

 early stages the small circular surface col- 

 onies have a wrinkled structure easily 

 demonstrated by magnification of twelve. 

 It grows well at 30° C. but not at all 

 at 37.5°. Its thermal death point is 

 over 48° and below 49.10° 0. It grows well 

 in Uschinsky's solution. In agar the 

 buried colonies are small. For this organ- 

 ism the name of Bacillus delphini is sug- 

 gested. The other bacterial spot diseases 

 mentioned as having come to the writer's 



