22 CEREAL RUSTS OF THE UNITED STATES. 



see how the fiingus luiglit be easily overcome.' At all events the writer 

 is convinced that the existence of volunteer wheat must have consider- 

 able bearing upon the distribution and propagation of this rust, and 

 the conviction will be strengthened should further experiments fail to 

 reveal other hosts besides wheat. There is still a possibility, however, 

 that some native grass harbors the same rust form. In Australia it is 

 generally accepted as a fact that both Puccinia rubigo-vera and P. 

 graminis exist in the "red rust" stage all the year through, either on 

 self-sown grain or on native grasses. Cobb (19, p. 29) and Lowrie (48, 

 p. 51) make particular references to the matter. However, it should 

 be remembered that identification on morphological grounds alone is 

 not sufficient to prove that the grasses mentioned actually bore these 

 cereal rusts and no mention is made of inoculation experiments. 



The observations made thus far in India do not indicate that this 

 rust lives the entire year in the uredo stage on any host. Barclay, 

 after careful investigation, failed to discover a continuous repetition of 

 uredospores (5, Vol. XXX, pp. 17, 48), though he admits the possibility 

 of such. He thinks such an occurrence more improbable than "in 

 Europe, where crops both of cereals and wild grasses overlap one 

 another." Prain (00, p. 27) and Watt (70, pp. 51-56) discuss this ques- 

 tion and accept Barclay's conclusions. 



Eriksson has failed to discover that any one of the wheat rusts lives 

 throughout the year in the uredo stage in Sweden. He claims to have 

 shown, however, that P. glumariim is perennial within the wheat plant 

 (25). To account for this he in^oposes a new theory, which will be 



' Dr. Geo. "Watt, editor of tlie Agricultural Ledger of India, makes quite unfavor- 

 able criticisms (70, pp. 55, 56) of the conclusions reached by Hitchcock and the writer 

 concerning this matter, as given on page 9 of onr second report on rusts of grain. 

 After quoting these conclusions he says: "The criticism would seem fairly justifi- 

 able, however, that the.se opinions are based on purely artificial experiments. The 

 experiments may, in fact, be said to show what might occur, not by any means what 

 occurs. It would, of course, be possible (under glass in cold countries or by reduc- 

 ing the temperature in tropical regions) to supply the parasite with continuous 

 crops of its host, and thus to produce uredospores for an indefinite period. * * * 

 The Kansas reports do not seem to afford sufficient evidence in support of the views 

 advanced. « * * In countries that do not have a severe climatic isolation between 

 the sea-sons of wheat cultivation, volunteer survivals of the crop might easily 

 enough occur. Where this is met with the existence of uredospores might be made 

 a matter of actual observation, and their vitality tested at repeated intervals, with- 

 out having to call in the aid of improbable experiments.'" But a more careful read- 

 ing of the bulletin will show that the "opinions"' mentioned are not "based on 

 purely artificial experiments," though greenhouse experiments were indeed employed 

 to confirm field observations. It is distinctly stated on page 2 of the report named 

 that the rust was observed in the field at diff'erent times, up to March 22, and of 

 course after that date rust would continue to grow in that latitude. In the mean- 

 time, to prove that in- these rust spots the spores were actually alive, many of them 

 were brought in at various times and germinated and healthy plauts infected with 

 them, thus "testing their vitality" exactly as Dr. Watt suggests should be done. 

 More than this, diseased plants were occasionally transplanted into the greenhouse, 

 and as fresh uredospores were produced befoie a period of incubation from inocula- 

 tions could have elapsed the mycelia were also shown to be alive (39, p. 2). 



