UNUSUAL RUSTS ON NYSSA AND URTICASTRUM ^ 
E. B. Mains 
(Received for publication February 25, 192 1 2) 
During the past year, two very interesting rusts of the family Melamp- 
soraceae have come to the writer's attention. The first of these, upon 
Nyssa aquatica, has remained in the form genus Uredo since its description 
in 1890 by Ellis and Tracy under the name of Uredo Nyssae. While pre- 
paring the manuscript of this species for the North American Flora, the 
writer was fortunate in discovering the telia. A study of this stage shows 
that the species can not be placed in any established genus and in conse- 
quence the following genus is proposed. 
Aplopsora^ gen. nov. 
Cycle of development imperfectly known, only uredinia and telia 
recognized, both subepidermal. 
Uredinia pulverulent; urediniospores produced singly, echinulate, the 
dores obscure. 
Telia lenticular, at first covered by the epidermis, soon becoming naked 
and cinereous from germination; teliospores one-celled, cylindric, in one 
layer, the wall thin, colorless, smooth, germinating shortly after reaching 
full size. 
Aplopsora Nyssae (Ellis & Tracy) comb. nov. 
Uredo Nyssae Ellis & Tracy. Jour. Myc. 6:77. 1890 
O + I. Pycnia and aecia unknown. 
II. Uredinia hypophyllous, scattered, round, minute, 0.1-0.3 mm. 
across, early naked, pulverulent, cinnamon-brown, ruptured epidermis 
inconspicuous; paraphyses peripheral, united below into a short, incon- 
spicuous pseudoperidium, clavate, incurved, 16-26 ijl long, the wall i ix 
thick, on convex side above up to 3-4 ^i, brownish-yellow; urediniospores 
obovoid or oblong, 13-17 by 16-26 ai; wall yellow or pale cinnamon-brown, 
I /z, rather closely and finely echinulate, the pores obscure. 
III. Telia hypophyllous, gregarious in small groups, round, small, 
0.2-0.5 mm. in diameter, at first covered by the epidermis, soon becoming 
naked, very pale translucent yellow, becoming cinereous from germination; 
teliospores cylindric, 7-15 by 29-40 /x, rounded above and below, in one 
layer; wall colorless, very thin, 0.5 }i or less, uniform in thickness, smooth, 
soon germinating with typical, external basidia. 
^ Contribution from the Botanical Department of the Purdue University Agricultural 
Experiment Station. Read in part before the Mycological Section of the Botanical Society 
of America at Chicago, December 29, 1920. 
^ Culture results revised to July i, 1921. 
^ From cLTrXoos, simple, and '^ccpa, scab, referring to the telium of one spore layer. 
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