60 COMPARATIVE MORPHOLOGY OF FUNGI 



them a line gradually degenerated as a result of submersed parasitism. 

 Hence the individual genera are considered in a series, descending in 

 respect to zoospore germination: first Myzocytium, in which zoospore 

 initials still arise within the sporangium, pass out as such into the germ 

 sac and there develop their flagella; then Lagenidium, in which the proto- 

 plasm partly flows out in a continuous stream through the emission 

 collar into the germ sac, and only there differentiates into the individual 

 spore portions; and finally Ancylistes where there is no differentiation of 

 zoospores and the emission collar, as the infection tube seizes new hosts. 

 These true Ancylistaceae are placed before Ectrogella. 



The better-known species of Ecirogella parasitize algae. The 

 commonest species, E. Bacillariacearum on diatoms, chiefly on Synedra, 

 is psychrophilic and occurs chiefly in spring and late fall. When a 

 zoospore reaches a host, it surrounds itself with a wall, and forces its 

 germ tube into a raphe. The thallus in time increases much in volume 

 and forces the valves of the diatom apart. The protoplasm of the whole 

 mature thallus collects at the wall (as in Olpidiopsis and the Saprolegnia- 

 ceae) and splits into zoospores which are liberated by a short, papilliform 

 emission collar. The zoospores have two short flagella of equal length 

 inserted in a lateral depression below the tip ; thus they are isocont. After 

 a short, not very intensive swarm stage, they come to rest and surround 

 themselves with a wall. Later, in the form of secondary zoospores, they 

 again slip out of this wall which they leave behind as an empty sheath. 

 Thereafter they possess a long and a short flagellum (and thus are heter- 

 cont) and are very actively motile. 



In other species, as in E. monostoma and E. Licmophorae, the first 

 swarm stage is considerably shortened. The primary zoospores collect 

 before the emission collar into a moriform group, shed their membranes 

 and swim away as secondary zoospores. Unfortunately these relation- 

 ships cannot be given diagrammatically in this book, as the work of 

 Scherffel only appeared after the figures were finished. One can picture 

 them approximately, however, if one imagines in Fig. 36, 9, a group of 

 empty zoospore membranes before the emission collar, as shown for 

 Achlya racemosa (Fig. 39, 1). 



E. monostoma and E. Licmophorae are thus related to E. Bacillariacea- 

 rum, as in the Saprolegniaceae Achlya is to Saprolegnia. In E. Bacil- 

 lariacearum, the shedding of the membrane of the primary zoospores 

 occurs as in Saprotegnia, far from the zoosporangium; in E. monostoma 

 and E. Licmophorae, as in Achlya, directly before its opening. 



This parallelism to the Saprolegniae goes farther in Ectrogella for 

 in E. Dickso?iii {Eurychasma Dicksonii, Rhizophidium Dicksonii), the 

 shedding of zoospore walls may take place in the interior of the zoospo- 

 rangium, thus leaving the empty walls inside the zoosporangium, as in the 

 net sporangium of Dictyuchus. 



