262 FARM FRIENDS AND FARM FOES 



The fact that the Cabbage Rot is caused by a bacterial 

 germ has been abundantly demonstrated. If you look 

 at cabbage leaves during a season of damp weather, you 

 will probably see a row of water drops along the margin 

 of each leaf. These have come out from small pores, 

 extending from the margin to the veins of the leaf. The 

 leaves are constantly giving off surplus water through 

 the pores ; in dry weather the water evaporates as it 

 emerges, but in moist weather it remains to form the water 

 drop. 



When one of the tiny bacteria carried in the air by the 

 wind happens to lodge in one of these water drops, it begins 

 to multiply, and soon develops in such numbers that the 

 bacteria enter the leaf through the water pore. Once in- 

 side, they travel down the veins, causing injury as they 

 go, until they reach the main stalk. They follow the large 

 channels in this stalk, and sometimes permeate the whole 

 head by pushing along through the system of veins. 



The injury done by these myriads of microbes checks 

 the growth of the plant and finally kills it. The germs of 

 other microbes soon enter the injured tissues and cause a 

 vile-smelling rot which effectually completes the work of 

 destruction. 



While the Cabbage Rot Bacterium is able to invade 

 healthy plants through the pores, it is often introduced 

 also by the bites of insects. If an insect is feeding upon 

 a diseased cabbage, its mouth parts are likely to be more 

 or less covered with the disease germs. If it then bites a 

 healthy plant, some of these germs will enter the tissues 

 of the latter, and the malady be started anew. 



The disease has proved very difficult to overcome. 

 Crop rotation and clean culture are helpful, but they are 

 by no means always effective. The selection of healthy 



