Arthur and Fromme: Value of Pore Characters 29 
in the teliospore is a racial feature rather than an acceptable mor- 
phological basis of separation. When both one- and two-celled 
teliospores occur together the generic assignment is arbitrary, it 
being understood that the two-celled spores are to be given prefer- 
ence, even if comparatively few, or if quite absent in part of the 
sori or on some hosts. The species may still be maintained in two 
genera for convenience and in conformity with usage. The deter- 
mination of the species, however generically disposed, on teli- 
osporic characters alone is often a difficult task and sometimes an 
impossibility, on account of the great similarity of the forms. 
It has become necessary, therefore, to utilize such other char- 
acters as are available and especially those of the urediniospores. 
Urediniospores can usually be found in collections of grass and 
sedge rusts even though no uredinial sori are present. A scraped 
mount made from a sorus of teliospores will usually contain a 
few of the other spores even if the collection be made at a season 
when uredinial production has apparently ceased. There are, 
however, three species of grass rusts, Piiccinia leptospora, P. 
Campitlosi and P. paradoxica^ in none of which have uredinio- 
spores been observed. These are rare species represented by 
single collections only. Teliospores, on the other hand, are by 
no means an omnipresent spore form of the grass and sedge rusts. 
They are seldom present in uredinial sori at the optimum growth 
period of the host, and in many species they are almost entirely 
wanting throughout the whole season, as in the common rust of 
blue-grass, Pticcinia cpipliylla, which produces teliospores in North 
America in alpine or boreal regions only. The urediniospore is. 
as a rule, the most abundant spore form and its characters are 
sufficiently constant and distinctive to make it of great value for 
taxonomic purposes. 
The most useful urediniosporic characters are : the form and 
size of the spore, the color and thickness of the spore wall, its 
surface sculpturing, and the number and distribution of the 
germ-pores. Among these the pore characters are perhaps the 
most valuable. The pores are usually visible in a water mount 
but it is often better to use a clarifying or staining agent to bring 
them out distinctly. A small drop of lactic acid mixed with the 
water in which the spores are mounted, especially if heated to 
