Arthur and Fromme; Value of Pore Characters 31 
vexans, a common rust of the prairies on species of Bouteloua. 
In addition to the normal thin-vvalled urediniospores this species 
produces a resting or amphisporic form of urediniospores. Tliese 
amphispores have a thick, dark-colored wall and are easily mis- 
taken for teliospores of Uromyces. They show their uredinio- 
sporic nature, however, by the production of a germ-tube in- 
stead of a promycelium, and by their ability to reinfect the same 
host. The normal urediniospores of this species have eight scat- 
tered pores, while the amphispores have four equatorial pores 
fFig. I, b and c). An explanation of the difference in number 
and position of the pores in the active and resting urediniospores 
should give a valuable insight into the evolution of this stage of 
the rusts. 
It is sometimes more difficult to ascertain the disposition of the 
the pores than their number. This is especially true in a globoid 
spore, as it is hard to be certain that it is properly orientated, but 
an ellipsoid or oblong spore will naturally lie upon the proper 
surface for convenient examination. Three general types of dis- 
tribution are recognized: scattered, equatorial, extraequatorial. 
The term scattered pores does not imply that the pores are 
without a definite arrangement. They are practically equidistant 
from each other over the cell surface in the typical scattered- 
pore condition (Fig. i, a, b and d). 
If the pores are equatorial, they more or less approximate the 
equator of the spore and are placed at about equal distances apart 
(Fig. I, e, /, g, and h). 
The extraequatorial group may be conveniently subdivided into 
pores superequatorial, and pores subequator ial. Like the equa- 
torial-pored condition these are zonal arrangements when more 
than one pore is present. The zone may be slightly above or be- 
low the equator (Fig. i, /), considerably above, near the apex 
(Fig. I, i), or considerably below, near the hilum (Fig. i, k 
and /). Two pores is the constant number for all of the extra- 
equatorial-pored species except those with pores near the hilum. 
One species, a grass form, Puc. Sporoboli, has three pores ar- 
ranged in a zone around the hilum, while two species, both sedge 
forms on species of Carex, each have a single pore near the hilum. 
The scattered- and equatorial-pored conditions are present in 
