6io 



MICROBIAL DISEASES OF PLANTS 



Others whicli are more difficult to follow. The nuclei first lose the 

 greater part of their chromatin and appear pale and indistinct, while 

 attraction spheres appear at the opposite poles of each. The« nuclei 

 then divide twice by karyokinesis and a small amount of cytoplasm is 

 separated off, constituting a gamete. The gametes now unite in pairs 

 and each pair becomes encysted to form a spore. 







®-^ 



Fig. i^g.^Plasmodiaphora brasslccB. A, a plant cell filled with parasites, the 

 nuclei of which are undergoing mitotic division (at the top is the nucleus of the 

 plant cell). B, two plant cells with developed and partly developed spores. {After 

 Prowazek, from Doflein.) - 



Whether during the multiplication of these organisms in the plant, 

 they are able to migrate to other cells and thus spread the infection has 

 been questioned. A number of investigators believe that the number 

 of infested cells is only increased by the division of the infected plant 



