114 



MYCOLOGY 



authors, are placed in the family Peronosporace^. Details of the 

 important forms which cause plant diseases will be given in the third 

 part of this book. These fungi will be referred to under each genus 

 following the systematic generic key which is here given. 



Generic Key of the Family. PERONOSPORACEiE 



Mycelium of these fungi parasitic or saprophytic in plant tissues; 

 zoosporangia as distinct organs producing biciliate zoospores. 



Zoospores formed out of protoplaem 



which escapes out of the conidia. i. Pythium. 



Zoospores formed within the zoosporangia. 



2. Pythiacystis. 



Zoospores elongate. 3. N emato sporangium . 



^_^ Mycelial hyphae branching non-septate 



/ ^ usually coarse, of strictly parasitic habit. 



Conidiophores short, thick, subepidermal, 

 conidia in chains. 4. Albugo 



Conidiophores longer superficial, simple 

 or branched, conidia not in chains. 

 Conidiophores scorpioid cymosely 

 branched conidiospores developing 

 swarmspores. 5. Phylophthora.^ 



Conidiophores simple, or branched 

 monopodially; conidia sprouting as a 

 plasma, or by swarm spores. Con- 

 idiophores regularly branched. 



Conidiophores simple erect with a 

 swollen end (basidia-like) bearing 

 short sterigma-like branches of equal 

 length. 6. Basidiophora. 



Conidiophores with lateral branches developed normally of 

 unequal length. Conidiophores stout, with few branches, 

 oospore united to wall of oogonium. 7. Sclerospora. 



Conidiophores slender, freely branched persistent; oospore 

 free. [ 8. Plasmopara. 



Conidiophores with forking branches; conidiospores sprout- 

 ing with a germ tube. Upper end of conidiospore with a 



Fig. 37. — White rust 

 Cystopus (Albugo) portula 

 cecB, on purslane, Portulaca 



oleracea 

 Harbor, 

 1915-) 



(Cold Spring 

 L. I., July 24, 



