30 
Mycologia 
the boiling point, is very effective, as is also the application of a 
solution of chloral hydrate and iodine. The latter is particularly 
serviceable when the spores are fresh and still retain their colored 
contents. These methods fail, however, in a few species having 
urediniospores with colorless or thick gelatinized walls. There are 
five of these species : three, Piiccinia versicolor, P. Boutelouae, and 
P. triarticulata, in which the pores are evidently scattered but the 
exact number cannot be made out, and two species, P. Seymouri- 
ana and P. Mclicae, in which neither the pore number nor distri- 
bution is known. 
According to our present knowledge there are 145 species of 
rusts on grass and sedge hosts in North x\merica having available 
pore characters; 105 species on grasses and 40 on sedges. The 
following account of urediniospore-pores is based upon this group 
of species, which includes those with both one- and two-celled 
teliospores. 
In the grass rusts the urediniospore-pores vary in number with 
the different species from 2 to 12. In species where the pores 
are restricted to the equatorial zone the most common number is 
3 or 4, and where the pores are scattered, 6 or 8. 
In the sedge rusts the range of variation, i to 5, is much smaller, 
five pores being the largest number known. The two-pored con- 
dition is most common and the one-pored condition, found in 
two species only, is rare. 
The extent of variation in number of pores in a single species 
is usually small. A variation of four, as from 8 to 12, is the 
extreme. Many species have a variation of two, as from 2 to 4, 
4 to 6, etc., or of one, as from 2 to 3 or 3 to 4, and in many the 
pore number is fixed. 
The real significance of the pore number from the physiological 
standpoint is not known and no theory to account for the presence 
or importance of more than one pore in each spore has been put 
forth. The pore number and distribution are no doubt associated 
in some way with the development of the species and possibly 
bear a physiological relation to the host. Their absolute hereditary 
constancy has never been proven. An apparent physiological mod- 
ification in the pore number and distribution is known in Pucinia 
