48 BACTERIAL DISEASES OF PLANTS 



In 1911 from Maryland carnations 1 and again in 1913 

 from Danish orchard grass 2 the writer called attention to a 

 new type of bacterial disease in which the principal growth of 

 the parasite is on the surface of the plant, that is between closely 

 appressed organs. Since then O'Gara has described a similar 

 disease from wheat-grass in Utah 3 and Hutchinson from wheat 

 in India, 4 See Fig. 35. 



THE REACTION OF THE PLANT 



We now come to the reaction of the plant. What response 

 does it make to this rude invasion? Twenty years ago we might 

 have said, "With rare exceptions, the plant is passive or nearly 

 so," but that would have been a superficial observation. In 

 every disease we must suppose that the plant makes some effort 

 to throw off the intruder, although often its forces are paralyzed 

 and overcome very early in the progress of the disease. 



One of the most conspicuous results is lessened growth In 

 some of my plants recovering from brown rot due to Bac- 

 terium solanacearum, 5 a month after external signs of the 

 disease had disappeared the check plants were twice the size 

 of the inoculated ones, and there was still a very decided dif- 



1 Smith, Erwin F. : " Bacteria in relation to plant diseases," Carnegie Inst. of 

 Washington, Publ. 27, Vol. 2, Fig. 4, Oct. 30, 1911. 



2 Smith, Erwin F. : A new type of bacterial disease, Science, n.s., Vol. 38. p. 

 926, Dec. 26, 1913. For a fuller account with figures see " Bacteria in relation to 

 plant diseases," Carnegie Inst. of Washington, No. 27, Vol. 3, pp. 155-160. 



3 O'Gara, P. J. : A bacterial disease of western wheat-grass, Agropyron Smilhii, 

 Phytopathology, Vol. 6, No. 4, August, 1916, p. 341. 



4 Hutchinson, C. M.: A bacteria! disease of wheat in the Punjab. Memoirs of 

 the Department of Agriculture in India, Agr. Research Inst., Pusa, October, 1917, 

 Bacteriological Series, Vol. 1, No. 7. 



5 Smith, Erwin F. : "Bacteria in relation to plant diseases," Carnegie Inst. \Vash- 

 ington, Publ. 27, Vol. 3, 1914, Plate 45-.D. 



O'Gara in 1916. The slime dries brownish yellow and masses of it may be seen 

 adhering to various parts of the spike; B. The same showing a knee-shaped culm 

 bending; C, D. Hutchinson's wheat disease of the Punjab (India) said to be due 

 to a polar flagellate schizomycete (Pseudomonas tritici Hutch.). All the spikelets 

 are stuck together or overgrown with a mass of lemon yellow slime. In D there 

 is bending of the culm. (After Hutchinson.) 



