Grass rusts of unusual structure* 
J. C. ARTHUR AND E. B. MAINS 
(WITH TWO TEXT FIGURES) 
The leaves of species of Olyra belonging to the tribe Paniceae 
and of species of bamboos are frequently much alike in form and 
physical characters, although systematists place the genera nearly 
at the extremes of the grass series. The resemblances are often 
so great that only an experienced agrostologist can feel sure of 
their identity when not accompanied by inflorescence. It is not 
surprising, therefore, that the rusts on these genera, as well as 
their hosts, should have been confused. Thus Uredo Olyrae 
P. Henn., described in 1904, to which true Olyra rusts have been 
referred, has recently been found to be on some species of the 
bamboo genus Arundinaria, and Uredo ignava Arth. on the genus 
Bambos has only recently been separated from material formerly 
placed with paniceous rusts. 
Not only is there a curious resemblance between the leaves of 
these two groups of hosts, but also an equally interesting re- 
semblance between some of the rusts that inhabit them. This 
was first noticed in the uredinia having delicate incurved para- 
physes and spores that are more or less thin-walled and colorless. 
Later it was found that the presence or absence of these weakly 
differentiated paraphyses is not by itself an important diagnostic 
character, as the forms called Uredo paspalicola without paraphyses 
and U. Stevensiana with paraphyses have been shown to be only 
extremes of one species having all degrees of intergradation. 
In the study of this sort of rusts it became more and more 
necessary to use a razor and make sections of the sori in order to 
be surer of their structure. In this manner the paniceous species, 
Puccinia tubulosa, P. inclita, and P. imposita, were segregated and 
gradually circumscribed from what had been lumped as P. sub- 

* Reprints may be obtained by application to the Botanical Department, Pur- 
due University Agricultural Experiment Station, Lafayette, Indiana, under whose 
auspices the studies here reported were carried out. 
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