1918] CURRENT LITERATURE 367 
conclusions are applicable not only to Uruguay but also to the adjoining prov- 
ince of Buenos Aires in Argentine, whose climate is similar to that of Uru ruguay. 
The geographical and ecological aspects of the subject are presented in two 
second treats of the influence of external factors on the occurrence of rusts. 
this long account only the salient features can be noted. 
Only 4 species of grain rusts occur in the La Plata region of age America, 
These are Puccinia graminis, P. triticina, P. coronifera, and P. : 
graminis infects strongly wheat, barley, and Lolium temulentum; less aca 
oats, Lolium perenne, Dactylis glomerata, and Alopecurus pratensis; while rye, 
European oats, Lolium multiflorum, and Phleum pratense are rarely infected. 
On other grasses it is not found. From cultures which seemed to indicate that 
this rust could be transferred from wheat to barley, and from rye, oats, barley, 
Lolium temulentum, and Dactylis glomerata to wheat, the author is inclined to 
believe that only a single biological race is present, which in its choice of hosts 
does not coincide fully with any of the established races. Although others 
have noted variations in the degree of fixity of biological races of rusts in 
different regions, it may nevertheless be assumed with reasonable certainty 
that further study will reveal more than one specialized form in the La Plata 
region, and that forms as distinct in other regions as that on wheat on the one 
hand, and that on oats and Dactylis glomerata on the other, will not be found 
to be identical in Uruguay. With regard to the occurrence of Puccinia graminis 
on the grain crops, it was found that the fungus was generally absent from both 
wheat and barley during the winter and spring. Some years wheat is entirely 
free from this rust, and in general the plants are not attacked until they are 
nearly mature, so that this rust is of little economic importance in the culture 
of wheat. It is the only rust that occurs on barley. Rye and oats are rarely 
attacked, but the native variety of oats suffers more severely than imported 
European types. 
Puccinia triticina occurs only on wheat and rye. It is found on wheat in 
the fields at all times of the year, and on plants of all ages, except in the earliest 
stages of growth. Infections on rye are rare and only uredospores are pro- 
duced. The opportunity to prove by cultures and observations that this rust 
occurs on rye was unusually favorable, because P. dispersa, with which it might 
be confused, does not occur in the La Plata region. 
Puccinia coronifera was found on Avena sativa, A. fatua, Lolium perenne, 
L. temulentum, and rarely on L. multiforum. The biolo, ical race on oats is 
- different from that on Lolium. A striking difference in susceptibility exists 
between native oats and European varieties. The native type is only lightly 
attacked, while the European varieties are entirely destroyed, so that their 
cultivation in this region is impossible. 
Puccinia Maydis occurs in Uruguay only on maize, and not on sorghum 
Maize is usually planted from October to January, and the rust begins to 
