888 AQUATIC PHYCOMYCETES 



walled, with a cellular envelope of periplasmic origin which fills the 

 oogonium or lies loosely in it, contents granular, with a large oil globule, 

 germination not observed. 



The species are all saprophytes on plant materials, particularly 

 floating twigs, and occur most commonly in late spring or early summer. 



Araiospora differs from Sapromyces and Rhipidium not only in the 

 curious production of spiny-walled and smooth-walled sporangia (Fig. 

 70 E-F, H) but also in the formation of a cellular envelope around the 

 oospore. King (1903) concluded after a morphological and cytological 

 study of A. pulchra that it shows definite affinities with the Peronospo- 

 rales and stands between Pythiwn and the Saprolegniaceae. Kevorkian 

 (1934) stated that in A. streptandra the fertilization tube is of antheridial 

 origin rather than formed by the ooplasm as King asserted (see also 

 under "Cytology," p. 865). 



Because of their symmetrical arborescent habit and exquisitely 

 reticulated often golden oospores these apparently rare fungi are one of 

 the most exciting "finds" among the water molds, and their delicate 

 beauty never fails to elicit the admiration of the collector fortunate 

 enough to secure them. 



KEY TO THE SPECIES OF ARAIOSPORA 



Spiny sporangia bearing numerous long slender spines either apically 

 or over entire surface 

 Oospore not filling the oogonium, antheridium diclinous A. spinosa, p. 889 

 Oospore filling the oogonium, antheridium monoclinous 



Antheridial hypha often branched, not twisted around the base of 



the oogonium A. pulchra, p. 891 



Antheridial hypha unbranched, twisted around the base of the 

 oogonium 

 Echinulate sporangia oval to pyriform; spines 10-15 \i long 



A. streptandra var. streptandra, p. 892 

 Echinulate sporangia spherical or nearly so; spines rarely less 



than 30 jj. long A. streptandra var. echinulosphaera, p. 892 



Spiny sporangia bearing a crown of from four to six short or slightly 



curved digitate apical spines A. coronata, p. 893 



