Order UREDINALES 
By JoSEPH CHARLES ARTHUR 
Small, mostly microscopic fungi, parasitic in the tissues of Pteridophyta 
(Filicales) and Spermatophyta. Mycelium much branched, septate, usually 
ramifying in the walls of the cells and extending haustoria into the cavities. 
Spores borne in more or less definite sori below the surface of the host, or 
rarely buried singly within the host, and set free by early rupture, or 
in case of some resting spores, by weathering away of the overlying tis- 
sues. Sori naked, enclosed by peridia or paraphyses, or imbedded in a thin 
stroma. Spores of five morphological sorts, not all present in every genus: 
(1) basidiospores, minute, thin-walled, without surface sculpturing, (2) pyc- 
niospores, small, smooth, of unknown function, (3) aeciospores, verrucosely 
sculptured, borne in chains, (4) urediniospores, echinulately or verrucosely 
sculptured, borne sitigly, or sometimes in chains (Coleosporium, Melampso- 
-vopsis), (5) teliospores, smooth or variously sculptured but not echinulate, 
borne singly or in chains. Pycniospores, aeciospores, urediniospores, and telio- 
spores follow each other in the order named; but any one or all, except the 
last, may be wanting in certain genera. An alternation of phases is conspicu- 
ously shown in many genera, the pycnia (rarely absent) with one other spore- 
structure composing the gametophytic phase, and the telia, usually with one 
other spore-structure, the sporophytic phase. In every species the mycelium 
eventually gives rise to teliospores, which produce in germination four basidia, 
either remaining within the spore-cell (Coleosporiaceae) or borne in the air on 
a short promycelium, each basidium supporting a single, stalked or sessile 
basidiospore. 
Basidia internal; teliospores compacted laterally into waxy layers; 
walls of spores weakly gelatinous. am. 1. COLEOSPORIACEAE. 
Basidia external. : 
Teliospores compacted laterally into a crust or column (rarely 
solitary within the tissues) ; walls of spores firm. . am. 2. UREDINACEAE. 
Teliospores free or fascicled; walls of spores firm, or with an 
outer hygroscopic layer, overlaid by cuticle. Fam. 3, AECIDIACEAE. 
VoLuME 7, Part 2, 1907] 83 
