oospoke-producing algai- fungi io9 



Key to Families of the Order Oomycetales 



A. Zoosporangia, oogonia and antheridia present; conidia absent. 



(a) Mycelium well developed. 



1. Antheridium forming motile spermatozoids, which enter the 

 oogonium. Family i. Monoblepharidace^. 



2. Antheridium not forming spermatozoids, fertilization through 

 an antheridial tube, or beak. Familj' 2. Saprolegniace^. 



(b) Mycelium poorly developed, sometimes represented by a single 

 cell. 



1. Fruit body as a single cell or by division forming a sporangia! 

 sorus; parasites on algae, protozoans, rarely on flowering 

 plants. Family 4. Chytridiace^. 



2. Fruit body through di\-ision a chain of cells which develop 

 sometimes into zoosjwrangia, sometimes into antheridia and 

 oogonia. Family 5. Ancyclistace.s:. 



B. Conidia present. Family 3. Peronosporace^. 



The following descriptions of the above five famiUes are presented 

 in order to introduce the student to the characters which fundament- 

 ally distinguish them. Therefore, all generic keys are omitted because 

 the introduction of them under each family would increase the size of 

 the book unduly. 



Family i. Monoblepharidace^. — This family is represented by 

 the genera Monoblepharis and Gonapodya . The genus M onoblepharis 

 is represented by two species of which M. spheerica is the most com- 

 mon. It is an aquatic fungus found growing saprophytically on dead 

 animal and plant parts under water. The hyphae of the mycelium 

 are tubular, branched and unicellular. The swarm spwres (zoospores), 

 which are formed much as in Saprolegnia, have only a single flageUum. 

 The oogonia are either terminal in position or interstitial and there is 

 no difiFerentiation of an outer periplasm, but the whole protoplasm 

 of the oogonium contracts to form an oosphere. Later a pore appears 

 at the apex of the oogonium through which the unicniate spermatozoids 

 enter to fertilize the egg cell. The antheridium in J/, spheerica appears 

 as a penultimate cell immediately below the oogonia. An opening is 

 formed at the top through which the sjjermatozoids escape. The 

 oosphere on fertilization becomes an oospore. Because of the aquatic 



