30 PLANT DISEASES 



The spores on germination give origin to amoeboid 

 bodies capable of exercising a sluggish movement. These 

 bodies coalesce in quantities to form a naked mass of 

 protoplasm, also capable of movement, called *. plasmodium. 

 This represents the vegetative stage. No mycelium is 

 developed during any period. The plasmodium eventually 

 becomes stationary, and resolves itself into a mass of 

 minute spores. 



Several organisms considered to belong to this group are 

 suspected as being parasitic on plants, the best known and 

 most destructive being the one causing * finger-and-toe ' 

 disease in cabbages, turnips, etc. (Plasmodiophora brassicae}. 



BACTERIA 



These infinitesimally minute organisms, popularly termed 

 ' germs ' or ' microbes,' are better known as the cause of 

 numerous animal diseases; in fact, it is only in comparatively 

 recent times that bacteria have been connected with plant 

 pathology. At the present day numerous plant diseases 

 are attributed to bacteria, some truly, others doubtfully so. 



Bacteria are distinguished according to their shape : 



(1) Cocci are spherical, either solitary or united in groups. 



(2) Bacilli are straight rods. 



(3) Spirilla are spirally curved rods. 



Numerous forms of bacteria possess the power of 

 voluntary movement, due to the presence of minute cilia 

 or flagella. 



Multiplication takes place in two distinct ways: (i) by 

 fission hence the name Schizomycetes sometimes given to 

 the group. When an individual has attained the normal 

 size it divides into two portions, each of which continues to 

 grow until the normal size is reached, when the process is 



