154 Illinois State Laboratory of Natural History. 
leaves the vegetative threads are seldom found at a greater lat- 
eral than vertical distance, the latter limited by the thickness 
of the leaf; yet the whole tissue may be permeated by the my- 
celium of different, perhaps very numerous, spores. 
In the preparation for the formation of spores, mycelium- 
threads become densely aggregated into a parenchyma-like 
tissue in a little area just beneath the epidermis, and from the 
upper surface of this minute cushion the spores are produced 
by the enlargement and modification of the end of a thread, 
either singly; or by the formation of septa, from two to several 
—in the latter case so as usually to form a single vertical row 
from each fertile filament. The clusters of spores (sori), 
usually very densely packed, are naked, or surrounded by pe- 
culiar sterile cells (paraphyses), produced from the mycelium 
or entirely inclosed in a membranous envelope (pseudoperid- 
ium), originating from the same source. By the growth of the 
fungus the epidermis of the host is pushed up and finally 
ruptured, so that the spores, mostly just at maturity, are exposed 
to the air, in the currents of which they are light enough to 
be carried as fine. dust. 
The species of Uredinee are limited to particular host 
species, mostly to one, or at farthest to the species of one genus 
or closely allied genera. None are certainly known to grow 
upon plants of different natural orders, except in the alterna- 
tion of fruit forms. In the latter case the teleutospores pro- 
duced upon grasses or sedges give origin, in some species, to 
zcidia on the leaves of certain exogens. In fact, it seems to 
be most common that when the ecidium is not grown on the 
same host with the uredo and teleutoforms, very wide diver- 
gence in this respect is made. Wheat and the barberry bush, 
oats and the buckthorn, red cedars and apple trees, are three 
examples of this remarkable peculiarity, the teleutoform in 
each case being found on the first named, the ecidium on the 
second. 
Following the descriptions of species in this paper, refer- 
ences are given for each species to the host plants, the locali- 
ties by counties (of Illinois), and the date of collection. The 
numbers in Arabic figures are those of the herbarium speci- 
mens, corresponding with those of the collector's notes; the 
