PERONOSPORALES 



195 



often much elongate vesicle, accumulates at its tip, and at 

 its rupture passes as an undifferentiated mass into the water, 

 finally breaking up there into swarmspores. Proliferation of 

 sporangia is of frequent occurrence. Their germination by germ 

 tube is unknown. The branch bearing the oogonium is charac- 

 teristically coiled around that bearing the antheridium. The 

 oogonium is globose or polygonal, and is almost completely 

 filled by the oospore which has a thick, hyaline, concentrically 





m^§[ 



Fig. 70.- — Pythiogeton transversum v. Minden. (a) Mycelium bearing three 

 sporangia, one empty and another showing the extrusion of the contents into a 

 tubuhir vesicle (fe). (c) Undifferentiated plasma after rupture of vesicle, {d) 

 Partially formed swarmspores. (e) Mature ciliated swarmspores. {After v. 

 Minden 1916.) 



stratified wall. The method of oospore germination is unknown. 

 The mycelium is of small diameter and is saprophytic in vegetable 

 substrata in the water. 



2. Pythium Pringsheim (1858). 



The genus Pythium was erected by Pringsheim on two aquatic 

 species, P. monospermum Pringsheim and P. entoyhytuvi Prings- 

 heim. The latter species was later transferred to Lagenidium 

 of the Ancylistales by Zopf. In Pringsheim's account the genus 

 is a member of the Saprolegniaceae, and as such was placed by 

 him in the algae. Other species were soon discovered and 

 described; P. grmcz7e Schenk in IS59, P. proliferimi de Bary in 1860, 



