74 PROTESTS AND DISEASE 



often run together forming large masses. In certain varieties 

 (e.g. Arran Chief) all resemblance to a normal tuber may be 

 lost, the entire tuber being transformed to a coralloid mass. 

 The warts are at first white, but as they become old they 

 begin to turn black and finally form a putrid mass from 

 which dark brown liquid exudes." 



The parasite was first described in 1896 by Schilbertzky 

 in Hungary as a chytridian. John Percival, Reading, 

 recognised it as a synchytrian and named it as above. 



A monograph by Dr. K. M. Curtis was published in 

 1921. It is a record of a very thorough biological study : 

 from it a scheme of the life of the organism can be con- 

 structed as is done for Sporozoa and other protists, Fig. 19. 



Curtis found that zoospores can live nearly a week in 

 an intact sporangium of S. endobioticum, if the sorus is not 

 ruptured. If water is added the sporangia burst and the 

 zoospores rush out. They are very active moving to and 

 fro for from 10 to 20 minutes. In 30 to 40 minutes move- 

 ment ceases, and unless they are in contact with a suitable 

 host-cell they disintegrate. 



Unripe sporangia need more time to discharge and the 

 zoospores are sluggish at first, and some die either in the 

 sporangium or near it. Living zoospores, Fig. 20, a, are 

 1 '5^ long and have a bright spot, the nucleus, at the anterior 

 end. 



It seems that zoospores from the same sporangium do 

 not pair. Before conjugation can occur a preparatory 



