152 



BACTERIA IN RELATION TO PLANT DISEASES. 



Plants attacked by this bacterial disease look as though hot water had been poured over 

 them. The foliage of the plants withers sometimes very suddenly all the leaves simul- 

 taneously. The leaf loses its fresh green color, becomes flaccid and droops, then dries up 



quickly. Usually the progress of 

 the disease is so rapid that the leaf 

 does not dry yellow, but retains a 

 dull black color. After the wither- 

 ing of the leaves, the leaf-stalk and 

 the stems also dry up, and soon 

 nothing remains but a dry mass of 

 stems and leaves. If pulled up, 

 the roots of such a plant are seen 

 to be colored brown, the side roots 

 being black and more or less rotten. 

 If the plants are not attacked in 

 an early stage of growth the fruits 

 show no signs of the disease exter- 

 nally, except in size, being some- 

 what smaller. When, however, 

 young plants become diseased, 

 their fruits often show brown spots 

 on the surface of the pods, the fruits 

 themselves being more wrinkled 

 than when normal and often 

 spongy, or with the seed decayed. 



Pi g- 70.* Neither the type of soil nor the 



altitude seems to have any connec- 

 tion with the disease. The disease occurs both on porous black soil and on stiff clay soil and it 

 is in the mountains as well as on the plains. It occurs in patches, rarely an entire bed being 

 affected. Sometimes it is on the borders of the beds, sometimes in the center. The first 

 signs of it do not appear until the crop 

 is 2 to 2.5 months old. It never ap- 

 pears until after the first weeding end 

 of the first month but it has also ap- 

 peared in undiminished virulence in 

 fields purposely left unweeded. It is a 

 root-disease, but does not seem to be due 

 to soil-infection, i. e., fields planted after 

 a diseased crop are not worse attacked 

 than other fields. If it ever spreads in 

 a concentric manner it is only after 

 it has become very well established. 



Microscopic examination of dis- 

 eased roots from 5 fields showed bac- 

 teria in large numbers throughout the 

 entire root-system, including the wood 

 parenchyma, and in advanced stages Fig. 71. f 



*FlG. 70. Bacterial disease of peanut (Arachis) from Java: A detail from the xylem part of fig. 69 to show the 

 morphology of the bacteria. Figure drawn by Katherine Bryan. 



fFlc. 71. Bacterial disease of peanut (Arachis) from Java: Cross-section of an immature petiole at the extreme 

 top of the plant showing bacterial occupation of the vessels and the formation of small cavities in their vicinity, the rest 

 of the tissues free. Drawn by Katherine Bryan. 



