KEY TO THE MORE IMPORTANT FAMILIES AND GENERA 71 



Hyphochytriaceae' : polycentric, intramatrical, forming a more or less branched 

 mycelium-like structure which here and there, terminally as well as in 

 intercalary positions, enlarges to form the sporangia or resting spores. 

 Two genera: Hyphochytriwn and Catenariopsis. 



Family Anisolpidiaceae. Anisolpidiwn resembles Olpidium very 

 closely in its life history except that sexuality has not been observed. 

 The pyriform zoospore possesses a long, anteriorly attached flagellum. 

 Two or three species parasitic in marine Phaeophyceae. In A. ectocarpii 

 Karling, the chromosome number is five or six in the dividing nuclei in 

 the sporangium. Reesia differs from the foregoing genus in the persistence 

 of the naked, amoeboid stage until the organism has attained almost full 

 size when a cell wall is produced. In R. amoeboides Fisch, the resting 

 spores arise from infection by bifiagellate zygotes formed by the union 

 of two swarm spores. Two species, parasitic in Lemna. (Fig. 22A-C.) 



Family Rhizidiomycetaceae. Rhizidiomyces resembles Rhizophydium 

 (or Phlyctochytrium, in one species, because of the presence of an apophy- 

 sis), but the zoospore is anteriorly uniflagellate, with the tinsel type of 

 flagellum. Four species are known, two saprophytic in soil, one parasitic 

 in algae, and one parasitic in the oogonia of Saprolegniaceae. Latrostium, 

 parasitic in the oogonia of Vaucheria, possesses only one recognized 

 species. The zoospores escape not through an exit tube as in Rhizidiomyces 

 but by the deliquescence of a large exit papilla. (Fig. 22D.) 



Family Hyphochytriaceae. Hyphochytrium infestans Zopf was first 

 described by its author in 1884 and has not been recognized since. It was 

 parasitic in the apothecium of a species of Helotium. It consists of an 

 extensive, coarse, tubular, branched, occasionally septate rhizomycelium 

 (or true mycelium?). The zoosporangia arise as terminal and intercalary 

 swellings on the mycelium. They open by a subapical orifice releasing the 

 anteriorly uniflagellate zoospores. No resting spores have been observed. 

 Two other species are known: H. hydrodidii Valkanov on Hydrodictyon 

 and H. catenoides Karling, mostly saprophytic. The former produces 

 resting spores. Catenariopsis possibly belongs in the foregoing genus. Its 

 difference appears to be a greater contrast between the enlarged zoospo- 

 rangia and the short connecting isthmuses. (Fig. 22E.) 



Key to the More Important Families and Genera of Order Chytridiales 



Holocarpic, i.e., endobiotic, without rhizoids, discharge tubes inoperculate. 

 Vegetative cell enlarging to form a single zoosporangium. 



Family Olpidiaceae 

 Zoosporangium not completely filling the host cell. 



Flagellum anteriorly attached but traihng posteriorly. (Doubtfully be- 

 longing in this family.) Sphaerita 



1 This family as here delimited differs greatly from the treatment accorded in the 

 first edition of this textbook, both as to its suggested relationship and contents. 



