LEPTO MIT ALES 889 



Araiospora spinosa (Cornu) Thaxter 



Bot. Gaz., 21: 326. 1896 



(Fig. 70 F, p. 890) 



Rhipidium spinosum Cornu, Bull. Soc. Bot. France, 18: 59. 1871. 



Basal cell broadly cylindrical, with rounded apex, in large plants up 

 to 800 [jl long by 160 \x in diameter, thick-walled, primary axes 780 \x 

 long by 76-96 \x in diameter, coarse, umbellate, unbranched, or giving 

 rise distally to secondary umbels, constricted and segmented only at the 

 place of origin or beneath the reproductive organs, rarely along the 

 filaments; sporangia usually borne in clusters or whorls of from two to 

 eight at the tips of the branches (rarely singly), occasionally directly on 

 the basal cell, smooth sporangia more or less narrowly ellipsoidal, 

 90-150 \x long by 45-60 \x broad, spiny type ovoid or broadly ellipsoidal, 

 100-150 [j. long by 40-80 u. broad, with an apical crown of solid rigid 

 straight or recurved spines 60-70 [jl long by 9 \x broad, of variable 

 number, often occurring in two whorls (the outer having up to eight 

 spines, the inner up to four) around the discharge papilla; zoospores 

 reniform, the two flagella attached in a lateral fold, contents granular; 

 antheridium relatively large, curved-cylindrical, appressed to the oogo- 

 nium along its whole length, borne at the tip of a long slender often 

 twisted and encircling branch usually of diclinous origin; oogonia 

 clustered on short segments, spherical, with a smooth brownish wall; 

 oospore spherical, not filling the oogonium, with a thick cellular wall, 

 germination not observed. 



On twigs, Cornu (loc. cit.), France; twigs of Quercus, A Inns, rhizomes 

 of water lily, Minden ( 1902: 822; 1915:593, fig. 10 [p. 590]; 1916: 151, 

 pi. 1, figs. 1-8), Germany. 



Aside from a brief statement by Cornu that certain sporangia 

 possessed long straight or recurved spines, our whole knowledge of this 

 species is due to the investigations of Minden. He not only studied the 

 plant in its natural habitat but obtained pure bacteria-free cultures on 

 plum gelatin decoction and liquid media. This has never been successfully 

 achieved by the few subsequent observers of this species of Araiospora. 



Minden's descriptions and figures indicate that the inner oospore w all 

 is very thin and appears to form the inner face of the peripheral cells. 



