LEPTO MIT ALES 891 



Araiospora pulchra Thaxter 

 Bot. Gaz., 21 : 328, pi. 23, figs. 20-25. 1896 

 (Fig. 70C-E, p. 890) 



Basal cell predominantly large, thick-walled, 800-1500 u. long by 

 25-50 u, in diameter, the apex subcylindrical or subconical, bearing 

 numerous secondary axes 275-2750 [jl long which are constricted and 

 septate at the base and repeatedly and umbellately branched distally, 

 the segments of the branches subcylindrical and becoming successively 

 longer and more slender, holdfasts coarse, much branched; sporangia 

 borne in whorls or umbels, smooth sporangia subcylindrical or broadly 

 clavate, 120-175 by 30-35 u., spiny sporangia broadly ovoid to pyriform, 

 60-70 by 45-48 a, the spines coarse, 10-35 u. long, radiating from the 

 whole surface of the sporangium; zoospores emerging singly or in a 

 mass; antheridium terminal, monoclinous, somewhat clavate, applied 

 at the base of the oogonium, borne on a recurved branched or unbranch- 

 ed segment; oogonia borne like the sporangia, pedicellate, terminal, 

 spherical, smooth-walled, 30-60 [i in diameter; oospore spherical, thick- 

 walled, golden, 35-45 u. in diameter, the contents with a single globule, 

 peripheral cells polygonal, about 7 by 10 \x, the whole completely 

 filling the oogonium, germination not observed. 



On twigs, particularly Fraxinus, Thaxter (F.) (loc.cit.), King (1903: 

 211, pi. 11 15), Sparrow (S., B.M.) (1932b: 296, pi. 8 f-g), United 

 States. 



The species occurs in association with Sapromyces and Monoblepharis 

 in late spring. It may form pustules, but more commonly occurs as 

 single plants. The cytology of the species has been investigated by King 

 (see p. 865). 



sex organs and discharged smooth-walled sporangia; D, detail of sex organs; 

 E, spiny and smooth-walled zoosporangia, one sporangium in process of 

 discharging its zoospores. F. Araiospora spinosa (Cornu) Thaxter, spiny and 

 smooth sporangia and sex organs. G. Araiospora streptandra Kevorkian, 

 sex organs. H. Araiospora coronata Linder, tip of sporangium showing crown 

 of spines around discharge orifice. 



(A-D, Sparrow, 1932b; E, Thaxter, 1896b; E, Minden, 1916; G, Kevorkian, 

 1934; H, Linder, 1926) 



