CHYTRIDIALES 423 



* Rhizidium leptorhizum Zopf, nom. nud. 

 Nova Acta Acad. Leop.-Carol., 47: 231, pi. 20, fig. 5 a-c. 1884 



No description in the text. Figures referred to appear to be of young 

 stages of Rhizidiomyces apophysatus. 



* Rhizidium spirogyrae Fisch, nom. nud. 

 Sitzungsber. Phys.-Med. Soc. Erlangen, 16: 56. 1884 



A binomial (unaccompanied by a description) used in mentioning 

 a form of Entophlyctis vaucheriae inhabiting Spirogyra. 



SIPHONARIA H. E. Petersen 



Journ. de Botanique, 17: 220. 1903 



(Figs. 4 V-W, p. 72; 26 C-F, p. 422; 27 F, p. 428) 



Mature thallus monocentric, eucarpic, consisting of a sporangial 

 rudiment (the body of the encysted zoospore), with or without an 

 apophysis, and broad, thick- walled, wide-lumened rhizoids; sporangium 

 inoperculate, formed from the sporangial rudiment; zoospores pos- 

 teriorly uniflagellate, with a single globule, formed in the sporangium, 

 discharged through a pore; resting spore borne like the sporangium 

 on the rhizoidal system, thick-walled, sexually formed after conjugation 

 of thalli by means of rhizoidal anastomosis, at germination functioning 

 as a prosporangium; contributing thallus (or thalli) remaining small 

 and rudimentary. 



Known only in insect exuviae. 



The sexual nature of the resting spore is characteristic of all species 

 of the genus. Karling (1945d) found fairly commonly in Siphonaria 

 petersenii that the rhizoid of the male thallus contacted the body of the 

 female directly; sometimes the male body itself became attached to that 

 of the female. 



Karling has postulated two types of life cycles for Siphonaria, one on 

 the supposition of genotypic sex segregation at meiosis in the germinat- 

 ing zygote (the most probable) and the other on the supposition of 

 phenotypic sex segregation at the close of the sporangial and zoosporic 

 period. 



