^ Wheat Rust in Australia. 



i wheat, when rains fall shortly after it has been cut, the second 

 growth or aftermath is almost always rusted, and so a second crop of 

 uredospores is produced. 



4 Since " intermediate hosts," such as the barberry, are not concerned 

 in Carrying over the rust from season to season, it has been suggested that 

 infi-tion may be communicated to the wheat from other grasses which, as 

 ave elsewhere shown, may also be attacked by Puccima gramims 

 Klebahn 1 (p. 230) has shown that uredospores from various grasses will 

 infect wheat, and it remains to be determined how far the grasses occurring 

 in our wheat-fields, and attacked by this rust, are capable of infecting it. 



c. Towards the end of the growing season, a second kind of spore is 

 produced, known as the teleutospore. It will not germinate immediately, 

 but onlv after a period of rest, and it may also aid in carrying over the 

 rust from season to season. But although it can germinate in the spring, 

 and produce other minute spores known as sporidiola, still they have not 

 been proved to infect the wheat-plant, and so we do not know what pur- 

 pose thev serve, if any. In other countries they a.re said to germinate upon 

 barberry leaves, and produce the aecidial form of the rustand it may be 

 that here they are simply dying out are becoming functionless, because 

 the barberry bush which they normally infect is not now available for them. 



6. There is still another way in which some rusts are propagated, and 

 that is by means of the threads of the fungus or mycelium remaining in- 

 side the seed and starting into life with the germination of the grain. But 

 although hundreds of seeds have been carefully examined by the micro- 

 scope, no trace of this has been found, and therefore for the present we 

 must decline to regard it as a probable cause. 



7. There still remains another possible means of continuation from sea- 

 son to season, which has been prominently brought forward by one who has 

 devoted considerable attention to the study of the rusts in Sweden, Profes- 

 sor Eriksson. Although he has not yet succeeded in giving scientific proof 

 of his theory, he considers that while infection by spores does occur, yet 

 the primary infection is from within, firom an internal germ of disease 

 inherited from the parent plant and latent in the seed. He grew wheat in 

 closed chambers, where it was believed to be secure against infection from 

 without, and still the rust appeared all the same, and he can only account 

 for this by supposing that in the cells of the seed the protoplasm is asso- 

 ciated with the plasma of the fungus what he calls mycoplasm and from 

 this there arises, if the conditions are favourable, the mycelium of the rust 

 fungus, quite independent of external infection^ He does not seem 

 to have considered the possibility of the spores of the fungus 

 being attached to the seed, and until the soil and the seed are thoroughly 

 sterilized and every precaution taken to exclude infection from without, 

 and the disease still produced, until then we must suspend our judgment 

 and accept the Scotch verdict of Not Proven. A very striking 

 case, however, that the seed may be the means of continuing 

 rusts from season to season is given by Carleton 3 in connexion 

 with Euphorbia rust (Uromyces euphorbiae, Cooke and Peck). The pods 

 of Euphorbia dentata, and even the naked seeds, were found to be affected 

 with aecidia, and on growing the rusted seeds under a bell- jar, those that 

 were disinfected produced plants without rust, while those not disinfected 

 gave rise to rusted plants. Here the seeds actually bore the aecidia, and 

 propagated the rust through the germinating seed. A similar instance is 

 met with in Aecidium platylobii McAlp., where the aecidial cups are borne 

 on the pods, and on opening the diseased ones, the seeds are frequently 

 found covered with the mycelium, which, on microscopic examination, is 

 found to penetrate them. 





