STTDIES ox CLUBROOT or CRUCIFEROUS PLANTS 449 



Spores germinate better after a slight rest period and in such a medium 

 as muck-soil filtrate. Each spore produces one swarm-spore, which, 

 if not supplied with a host, develops no further. 



It is difficult to stain the flagella of swarm-spores, but if they are first 

 killed instantly with fumes of osmic acid fairly good mounts can be 

 obtained. 



Penetration takes place thru the wall of the root hair while the organism 

 is in a uninucleate stage. The root hair at once shows hypertrophy. 

 The amceba increases in size as it passes rootward, and finally, by direct 

 cell- wall penetration as well as by the division of the host cells, the patho- 

 gene is distributed thruout the cortical tissue. 



The spores are not always formed by simultaneous vacuolar divisions 

 of the amoebas, there being cases in which they are produced by successive 

 divisions while the adjoining amcebas may still be in the nuclear stage. 



Aside from Plasmodiophora Brassicae, there is often present another 

 organism, which causes no hypertrophy and which is probably Olpidium 

 Brassicae (Wor.) Dang. 



In the experiments to determine the relation of bacteria to Plasmo- 

 diophora Brassicae, a large number of isolations were attempted, diseased 

 tissues of all stages were stained, spores were germinated in sterilized 

 media, and infections were secured in test tubes under aseptic conditions. 

 All this points to the fact that the bacteria do not enter the host as soon 

 as the slime mold does, but follow only after there has been enough enlarge- 

 ment of tissues to rupture the epidermis. Consequently the bacteria 

 can be of no vital importance in the nutrition of the parasite. 



