40 THE LOWER FUNGI— PHYCOMYCETES 



septa to function as reproductive organs; the remainder of the thalhis 

 retaining its vegetative character; sexual reproduction usually present; 

 resting spores, identical in aspect with the sexual spores, developed in 

 some genera parthenogenetically. 



A. Male and female gametangia freeing ciliate gametes which fuse to 



form zygotes; zygote developing directly into the new plant 

 without first becoming a resting spore; characteristic thick- 

 walled chlamydospores formed asexually. 



3. Blastocladiales, p. 130 



B. Female gametangium not forming ciliate gametes; sexual fusion 



resulting in a thick-walled resting spore. 



1. Contents of female gametangium differentiated at maturity 



to form one or more naked protoplasmic spheres termed 

 oospheres; sexual identitj^ of male and female gametangia 

 evident; female gametangium (oogonium) larger and 

 stouter than the male gametangium (antheridium); true 

 gametangial copulation lacking; fertilization accomplished 

 by passage of one or more male nuclei directly into the 

 oosphere; oosphere maturing into a thick-walled oospore 

 lying free in the oogonium; swarmspores formed in most 

 genera. — Oomycetes. 

 a. Antheridium forming ciliate cells (antherozoids) which 



swim to the oogonium and fertilize the oosphere; 



fertilization tube lacking. 



4. Monoblepharidales, p. 138 



6. Antherozoids not formed; one or more male nuclei 

 discharged into the oosphere through a fertilization 

 tube put out by the antheridium. 



(1) Forms typically aquatic and chiefly saprophytic; 



sporangia usually not deciduous, freeing 

 endogenous spores; asexual cells functioning as 

 conidia uncommon; oogonium forming one to 

 many oospheres. 



5. Saprolegniales, p. 146 



(2) Forms typically terrestrial and parasitic, though 



species of aquatic, semiaquatic, and saprophy- 

 tic habit occur; sporangia typically deciduous 

 and wind disseminated, commonly termed 

 conidia, in some cases freeing endogenous 

 spores, in others germinating directly by germ 

 tube; oogonium forming a single oosphere 



6. Peronosporales, p. 185 



2. Oospheres lacking; sexual identity of male and female 



gametangia not evident; the two cells usually indistinguish- 

 able in size and shape, and functioning alike; consequently 

 the terms antheridium and oogonium not applicable; true 

 gametangial copulation occurring and the merged proto- 

 plasts transformed into the zygospore; zygospore not lying 



