288 



BACTERIA IN RELATION TO PLANT DISEASES. 





a- 



\ 



\ 



i\ 



Fig. 82* 



The organism occurs singly, in pairs, and more rarely in fours joined end to end. Long 

 chains and filaments have not been observed. Pseudozoogloeae or flocculent particles do 

 not occur quickly in bouillon, but compacted masses have been observed on plates, etc., and 

 they occur in the plant. Usually in fluid cultures no rim or pellicle is formed, but there may 

 be flocculence in some liquids, e. g., Uschinsky's solution, though 

 this is often wanting. Spores are not known to occur. This organ- 

 ism is a white, wet-shining, schizomycete, motile by means of 4 to 8 

 peritrichiate flagella (fig. 84). In young cultures motility is easy 

 to observe. It has also been observed in slime taken directly from 

 the vessels of the cucumber, melon, etc., and diluted with sterile 

 water. In the plant motility is easier to observe in rods taken from 

 tissues recently invaded than in those taken from crowded vessels. 

 Involution forms occur in the plant and in various media beet-juice, 

 cucumber-juice, peptone-water, potato broth (vol. I, fig. 21), etc. 

 On steamed potato the growth is white and so closely like the 

 substratum in color that it is scarcely to be distinguished therefrom 

 except by its smooth, moist, glistening appearance. It has very little action on potato- 

 starch, even very old potato-cultures reacting strongly with iodine. It does not soften the 

 middle lamella of potato-cells. Potato-cylinders may or may not be grayed. In one experi- 

 ment the organism remained alive on 

 potato over seven months (16 to 18 

 C), but usuallyit is dead muchsooner. 

 In one set of experiments no 

 growth was obtained on red turnip-rooted table-beets, nor on turnip-roots, radish-roots, 

 or cauliflower-petioles. When these experiments were repeated some years later the fol- 

 lowing results were obtained: On the beets growth was delayed but finally appeared. It 



was visible in one tube on the sixth day, in another 

 on the fifteenth day, and in a third on the twenty- 

 second day; the fourth tube remained sterile. Similar 

 results were obtained by a repetition of the experi- 

 ment: There was marked retardation of growth as 

 compared with that in the agar-stab, none being 

 visible on the beets the fourth day; on the thirteenth 

 day there was a visible growth in one of the tubes but 

 not in the other, on the twentieth day a typical 

 growth appeared in the second tube. Upon radishes 

 similar results were obtained, viz., marked retarda- 

 tion but final growth in most of the tubes. No 

 growth was obtained on turnips (two sets) and only 

 a doubtful growth on cauliflowers. 



In 1896, inoculations were made into the juice 

 of red table-beets filtered sterile and used both with and without the addition of calcium 



Fig. 83.t 



fj* 



Fig. 84.: 



*Fig. 82. Bacteria from interior of cucumber-stem at time of general wilt of foliage, but while main axis was still 

 green and normal in appearance (plate i, tig. 2); bacteria were present in vessels in enormous quantities. The great 

 mass of them were of size and shape of 2, those of size 1 being seen only occasionally. Drawn unstained with Abbe 

 camera, Zeiss 3 mm. 1.40 n. a. apochromatic objective, and No. 18 compensating ocular. Anacostia, D.C., July 15,1893. 



tFio. 83. Free-hand drawings of paired rods of li. tracheiphilus which have lost their flagella. Stained by van 

 Hrmcngem's nitrate of silver method in April, 1895, and measured after lying in balsam until Oct., 1895. Size of organ- 

 ism appears greater when stained in this manner than when stained without flagella-mordants. Very careful measure- 

 imnts of one member of each pair gave following result in microns: 2.03X1.05; 2.10X0.98; 2. 55X1. 10; 2.18X1.05; 

 2.75X1.20; average 2.32 X 1.08. Circa X1500. 



G. 84. Camera drawing from cover-glass preparation of young culture of B. tracheiphilus stained by van 

 Ermengem's nitrate of silver method. Flagella distinct; hundreds on cover-glass. Some rods with only one or two 

 left, others with as many as 8; most bear about 6. An occasional flagellum is 10.5 // long; most are shorter. Oct. 4, 

 1895. Circa X 1500. 



