CHYTRIDIALES 511 



Both forms have been observed in Michigan material, but neither 

 has been convincingly connected with the sporangial stage of the species. 

 Careful observations on the second type of spore, which, as Scherffel 

 suggests, probably belongs to a parasitic organism, reveal minute spines 

 in addition to the reticulations on the outer wall. 



The reactions of the host to the incursions of the fungus are very 

 marked and involve the formation of conspicuous protective plugs of 

 cellulose on the walls wherever the vegetative system attempts entry. 

 Scherffel has noted that, in this reaction, the nucleus of the alga is drawn 

 away from its central position in the cell and, with a concentration of 

 plasma, takes up a position close to the attacked cross wall. This, he 

 asserts, lends support to the idea that the nucleus plays a role in wall 

 formation. Under high magnifications it can be clearly seen that the 

 protective plug when penetrated by the fungus is not pierced in a single 

 place but in several. It is possible that the fungus is unwalled when 

 passing through these plugs. 



In the American material early stages in the development show that 

 the rhizoid is well established before the apophysis makes its appearance. 

 Although Scherffel states that no central vacuole is formed in the spo- 

 rangium during the process of maturation, it has been observed in a 

 number of instances in the Michigan material. 



Rieth (1951), who made a careful study of this species, noted that 

 the zoospores which germinate free in the medium will become trans- 

 formed into small thalli and from the sporangium of each a single zoo- 

 spore will be produced. He also observed extramatrical resting spores, 

 associated with the sporangial stage, which were essentially like the 

 unhorned ones previously reported by Scherffel (1925b). As in the 

 latter's Hungarian material, each spore was resting on an epibiotic, 

 small, empty cell, a phenomenon suggesting a type of sexuality like 

 that in Rhizophydium ovatum. In that species the male is epibiotic and 

 remains small, the female attaches to it distally, receives the contents 

 of the male and expands into a resting structure. If this type of resting- 

 spore formation is ever definitely connected with the sporangial stage, 

 Chytridium eonfervae should be segregated from the genus Chytridium. 

 Its strongly hypha-like vegetative system ramifying through many cells 

 of the host and the extramatrical resting spores would be sufficient 

 grounds for separation. 



