426 



BULLETIN 387 



It has been difficult to properly fix swarm-spores for staining flagella. 

 The first method of staining tried was that ordinarily employed for bac- 

 teria, namely, LoefHer's mordant and Ziehl's carbol fuchsin. When 

 bacteria were in the mount their flagella were stained, but those of the 



swarm-spores had evi- 

 dently disappeared. The 

 process was then modi- 

 fied slightly, and the 

 cover-glass mounts, in- 

 stead of being left .to 

 dry in the incubator* 

 were placed on slides in 

 preparation dishes with 

 ground-glass tops. In the 

 bottom of each dish was 

 placed a few cubic centi- 

 meters of osmic acid, and 

 the lid was then carefully 

 fitted in place. The acid 

 killed a few of the swarm- 

 spores before the flagella 

 could be withdrawn, but 

 never a very large pro- 

 portion. Besides demon- 

 strating the presence of 

 flagella, the stained ma- 

 terial also displayed 

 different stages of ger- 

 mination (fig. 97). 



Kunkel (1915) was able 

 to get spore germination 

 of Spongospora subter- 

 ranea on an agar me- 

 dium. Plasmodiophora 

 Brassicae evidently does 

 not react in the same 

 way. During the three 

 years of the present work, repeated efforts were made to secure not only 

 germination on the surface of agar, but also formation of plasmodia. 

 Unless the spores were immersed in water there was no development. 

 They lay there until the agar became so dry that they finally lost their 

 viability. If enough of the muck-soil filtrate was added, the swarm- 



FlG. 97. SPORES AND SWARM-SPORES OF PLASMODI- 

 OPHORA BRASSICAE 



The two spores at the top have already germinated. The germi- 

 nating spore and the two swarm-spores near the bottom were drawn 

 from stained mounts. The bacillus shown is the form found oftenest 

 in older diseased roots. x 2100 



