THE SYNCHYTRIAN NUCLEUS 85 



At this stage some of the granules, now zoospore-origins, 

 or " primordia," show signs of subdivision. Later still the 

 plasm of the primordia becomes vacuolated and granules of 

 chromatin are expelled, i ; by this process the primordia 

 become equal and spherical and their chromatin is reduced 

 to a few granules, from which the single nucleus of the 

 zoospore is formed. The young zoospore's plasm first 

 becomes dense, then vacuolated, j. The nucleus in the 

 zoospore has a clear central area with chromatin granules 

 around it, k, and a chromatic strand stretches from it to 

 the blepharoplast at the opposite end of the body of the 

 zoospore. 



A species of Synchytrium in a Thistle. For an oppor- 

 tunity of studying some aspects of the cytology of Synchy- 

 trium and of comparing it with such records as I have read 

 and with the structure of Plasmodiophora and Mycetozoa I 

 am indebted to the kindness of Professor V. H. Blackman 

 and Assistant Professor R. J. Tabor of the Imperial College 

 of Science and Technology. 



The host-tissue was a thistle-leaf 1 which had been fixed 

 in 95 % alcohol. With a pocket-lens the parasites were 

 seen as brick-red points. Sections were cut for me by 

 Dr. Perkins and stained with H. and E. Some of the 

 results are shown in Fig. 23. 



The walls of the host-cells are thick and stain deeply as 



1 Not having been able to identify the species of either host or parasite in this 

 instance I refer to the parasite in what follows as the thistte-Synchytrium. 



