66 BACTERIA IN RELATION TO PLANT DISEASES. 



With Bacillus tracheiphilus, inoculating from young agar-cultures, potato-cultures, or 

 bouillon-cultures into the leaf-blades of cucumbers and other very susceptible plants by 

 means of needle-pricks, the writer has seldom been able to obtain signs of the disease in less 

 than 3 or 4 days. Usually the first signs (wilt and change of color in the vicinity of the 

 punctures) were visible in 5 to 7 days. Occasionally the wilt did not appear until after the 

 tenth day, once it was not manifest until after 21 days, and once not till after 30 days. 



In leaves of hyacinths inoculated by needle-pricks with Bacterium hyacinthi signs of 

 the disease appeared in from i to 3 weeks. 



In one experiment in cabbage leaves inoculated by way of the water-pores with Bac- 

 terium campestre, the serratures of the leaves showed a distinct blackening within 4. to 6 

 days, but a period of 3 weeks elapsed before there was any visible spread of the disease down 

 the leaf, i. e., away from the leaf -serratures. In another experiment there was a distinct 

 blackening in the region of the water-pores in 6 days. In Russell's water-pore infections on 

 cabbage, signs appeared in 2 to 3 weeks. Stem-inoculations, i. e., needle-punctures without 

 injection, cause signs of the disease in the nearest leaves, viz., yellowing, flabbiness, and 

 brown veining after 7 to 28 days (Smith, Harding, Hecke). 



In sweet corn infected in the seedling stage by Bacterium stewarti, a period of i, 2, or 3 

 months may intervene between the first signs of disturbance in the seedling leaves and the 

 general sickening of the plant, during which, of course, the plant has grown to many hundred 

 times its original weight. There may be an equally long period between local infection and 

 constitutional disturbance in case of sugar-cane attacked by Bacterium vascularum. 



In Savastano's experiments with the olive-tubercle, knots began to appear upon the 

 young shoots in a little over a month after puncture and were well developed in 2 months. 

 In my own and Mr. Rorer's experiments, incipient knots were frequently visible as early 

 as the end of the second week, i. e., sufficiently developed to be distinguished from the 

 control punctures, and were very distinct in a month, but larger, of course, after several 

 months (see vol. I, plate 2). Once in a later experiment, starting with cultures very recently 

 plated from a knot and introducing the organism by needle-pricks from agar, I observed 

 the beginnings of tumefaction on 5 shoots as early as the ninth day. 



In case of the soft-galls, due to Bacterium tumefaciens, the writer has sometimes obtain- 

 ed the distinct beginnings of them as early as the third or fourth day, using pure cultures, 

 needle-punctures, and very susceptible tissues such as young shoots of the Paris daisy. 

 Earlier than this it is not possible to decide whether the slight swellings are to result in 

 tumors or are simply a reaction of the plant to the needle-thrust. Ordinarily if the organism 

 is virulent, the tumors are distinctly visible in 8 or 10 days if the tissues are young and 

 tender, but they continue to grow for several months, or even many months. 



The bacterial leaf-spot diseases are usually visible in i to 2 weeks from the date of 

 inoculation. 



DURATION OF DISEASE. 



Plants show very different degrees of resistance to a bacterial organism once ensconced 

 in the tissues. The soft -rot organisms, as already noted, are usually prompt in their action, 

 and a week or two is often sufficient to destroy the susceptible parts. The writer has seen a 

 good-sized potato-tuber half rotted in 5 days at ordinary autumn temperatures when 

 inoculated with Bacillus phytophthorus by means of a few needle-pricks, this too, in a rather 

 dry air; others wholly rotted in 8 or 10 days. Under favorable circumstances, inoculating 

 from a young agar-culture, the flesh of a melon one decimeter in diameter may be rotted 

 wholly by Bacillus melonis in 4 or 5 days (Giddings, Smith). In case of the leaf-spots, 

 progress is much slower, and the disease is generally restricted to small areas, e. g., bacterial 

 leaf-spot of the peach, which dry out and fall away from the sound tissue, especially if 

 excised by a cork layer. After plain signs appear, a week or two is sufficient in most cases 

 to accomplish the destruction of the affected part. In cucumbers and muskmelons attacked 



