CHYTRIDIALES 



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Fig. 18.^ — Synchytrium endohioticum (Schilb.) Percival. (a) Uninucleate 

 thallus. (6) Thallus functioning as a prosorus; its contents streaming out into a 

 thin-walled vesicle, the sorus. (c) Uninucleate sorus. {d) Sorus plurinucleate 

 by division of primary nucleus, (e) Cleavage planes have divided the sorus 

 into sporangia and repeated nuclear division has occurred. (/) Mature sporan- 

 gium; papilla of dehiscence forming, {g) Three mature sporangia in a common 

 soral membrane; swarmspores escaping; the old prosoral envelope flattened 

 against the host wall, (k) Two gametes in contact, (m) Binucleate zygote 

 following fusion, (n) Zoospores encysted on host wall; the cilia have dis- 

 appeared and nuclear fusion has occurred, ip) Infection by zygote, (s) 

 Young resting sporangium, {t) Epidermal region of gall containing resting 

 spores (resting sporangia) near maturity. {After Curtis 1921.) 



