KEY TO THE FAMILIES AND GENERA OF ORDER BLASTOCLADIALES 91 



from the eucarpic, monocentric, inoperculate Rhizidiaceae, through 

 Blastocladiella, Allomyces, and Monoblepharella to Monohlepharis, with 

 the uninucleate vegetative body in the more primitive forms becoming 

 transformed directly into a zoosporangium or gametangium, as in 

 Rhizophydium, while in Blastocladiella the vegetative structure is ovoid or 

 elongated with many nuclei, bearing the reproductive organs terminally. 

 Here the motile gametes are isogamous. In Allomyces the plant body is 

 more hypha-like and branched, and the reproductive organs are numer- 

 ous. In section Euallomyces the motile gametes are heterogamous. In 

 Monoblepharella the female gametes are one to eight in the oogone and 

 are motile, not by their own flagella, but by means of the flagellum of 

 the sperm. In Monoblepharis the egg is single in the oogone and is not 

 at all motile except in the species with exogenous oospores, where it 

 creeps out of the oogone after fertilization but has no power of further 

 locomotion. 



Key to the Families and Genera of Order Blastocladiales 



Plant body at first tubular, coenocytic, then forming alternately zoosporangia 

 and narrow isthmuses. Rhizoids arising at isthmuses or at all points. Resting 

 spores formed sometimes in place of zoosporangia. 



Family Catenariaceae 



Only genus. ^ Catenaria 



Plant body coenocytic, branching and anastomosing, apparently without a cell 

 wall in its vegetative stage, multinucleate. Tips of the branches enlarging 

 to form thick-walled resting spores with the outer wall marked punctately 

 and with longitudinal lines. These produce posteriorly uniflagellate zoospores 

 soon, or after a resting period in the dry state. Parasitic in the larvae of 

 mosquitoes. Family Coelomomycetaceae 



Only genus. Coelomomyces 



Plant body with basally attached tuft of branching rhizoids and a globular or 

 clavate external basal segment upon which directly, or upon branches of 

 which, arise the reproductive organs (zoosporangia, resting spores, game- 

 tangia) . Sometimes the distinction between the basal piece and the branches 

 arising from it is only slight. Family Blastocladiaceae 



Plant body with a simple or lobed or branched basal portion, often with sec- 

 ondary axes. Zoosporangia with single apical exit papilla. Alternation of 

 sporophytic and gametophytic generations unknown. Sexual reproduction 

 mostly unknown. Blastocladia 



Plant body a more or less spherical structure which is directly transformed into 

 a reproductive organ, or more or less clavate, bearing at its top a single 

 reproductive organ. Discharge papilla one or several. Alternation of gen- 

 erations demonstrated in some species. Blastocladiella 



Plant body consisting of a cylindrical basal segment giving rise — usually 

 dichotomously — to cylindrical, often constricted, branches with pseudo- 

 septa at the constrictions. Usually more than one discharge papilla. Sexual 

 reproduction by anisoplanogametes or isoplanogametes. Alternation of 

 sporophytic and gametophytic generations known in some species. 



Allomyces 



