THE SYNCHYTRIAN NUCLEUS 89 



features of this infected thistle-leaf with those described by 

 Curtis in the potato. 



Apart from the want of a " rosette " and there being no 

 evidence of cell-proliferation on part of the host-tissue, 

 the formation of the sorus and the character of the nuclei 

 in the nearly ripe soral sporangia is the same in the two 

 parasites. 



Very different is the rest of the picture ; and yet the 

 character of the nucleoli, and the processes of chromidium- 

 formation show that the direct sporangium in this thistle- 

 Synchytrium corresponds with that sporangium of 8. endo- 

 bioticum that developes from a zygote. 



Stages of the two may be compared as far as a very 

 partial examination of the thistle- Synchytrium allows. Fig. 

 23 is reproduced from the " Lancet," vol. ii. p. 495, 1921. 



In the thistle- Synchytrium at a certain stage no separate 

 chromatin points are to be seen, so the term " plasson " is the 

 one I would suggest to describe the state of the sporangium 

 as shown in Fig. 23, d and e. It becomes chromidium 

 at the later stage, /. The terms plasson and chromidium 

 are used here as defined above, Chapter I, pp. 4-6. 



The Synchytrian Nucleolus. The nucleolus is the 

 dominant cell-organ in Synchytrium ; from it are developed 

 the chromidia ; vegetative in the agamic, generative in the 

 gamic stages ; and in the former also the chromosomes and 

 spindle. The nucleolus is the centre of growth as well as of 

 reproduction in Synchytrium. 



