396 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



attacked by the bacterial bud-rot. Knee-shaped curvatures 

 of the culms appear on Dactylis attacked by Aplanobacter 

 Rathayi, and in the buds of the sugar-cane attacked by Cobb's 

 disease. 



Organs may be developed in excessive number or out of 

 place, as roots in hairy-root of the apple, witch-brooms on 

 Pinus, and incipient roots on the stems of tomato, tobacco, 

 chrysanthemum, nasturtium, etc. Hunger found a bud on a 

 tomato leaflet which he attributed to the stimulus of Bac- 

 terium Solanacearum. 



In various diseases the plant removes starch from the vicin- 

 ity of the bacterial focus which it endeavors to wall off by the 

 formation of a cork barrier, and in this effort it is sometimes 

 successful if the parasite is growing slowly. 



The most conspicuous response of the plant is in the form 

 of pathological overgrowths, — cankers, tubercles, and tumors. 

 Some of these are very striking, e. g., those on the ash, olive, 

 pine, oleander, and on a multitude of plants attacked by crown- 

 gall. In some of these growths there is a great reduction of 



the vascular system, and a great multiplication and simplifica- 

 tion of the parenchyma. There are also various other phe- 

 nomena nearly related to what takes place in certain insect 

 galls. In crown gall cell division under compulsion proceeds 

 at such an abnormally rapid rate that the cells are forced to 

 divide while still immature, and in this way masses of small- 

 celled unripe (anaplastic) tissue arise. These develop tumor- 

 strands on which secondary tumors arise. 



PREVALENCE AND GEOGRAPHICAL DISTRIBUTION 



Economically considered, bacterial diseases of plants may be 

 classed as major or minor. Most of the leaf-spots would fall 

 into the latter class. Various soft rots, blights and vascular 

 diseases, being wide-spread and destructive to plants of great 

 economic importance, may be classed as major diseases. 

 Cankers and tumors would fall midway in such a grouping. 

 Occasionally a minor disease, e. g., lettuce rot, celery rot, 

 under favorable conditions may assume great importance. 



