66 



Wheat Rust in Australia. 



begins to form the grain, and if that season is favorable for the develop- 

 ment of rust, then the fungus has to draw upon the stored-up material, and 

 consequently the grain is not fully formed, if at all. Incidentally this 

 investigation also throws light upon the reason why the earlier rust (P. 

 iriticind) is comparatively harmless, since its period of greatest activity^ is 

 when root and leaf are busy manufacturing material sufficient to provide 

 for the necessities of both. 



On account of the comparatively late appearance of P. gramtnis, it is 

 by some considered to do the least damage to the grain, but, as a^ matter 

 of observation, and on physiological grounds, it is known, at least in Aus- 

 tralia, to be the most injurious. 



\ 



PUCCINIA GRAMINIS AND THE BARBERRY IN AUSTRALIA. 



In Europe and America the identity of P. graminis is determined, not 

 merely from its morphological characters, but from its ability to infect the 

 barberry and produce aecidia. But in Australia infection of the barberry- 

 has not been successful, although several attempts have been made, and 

 some have doubted whether we have got the true P. graminis, and not a 

 distinct biological form of it. From a comparison with European speci- 

 mens and a critical examination of the sori, the uredo and teleuto spores, 

 there is no doubt that the rusts are very much alike, only if the infection of 

 the barberry is accepted as a diagnostic character, then the identity is not 

 proved. The relation of this rust, therefore, to the barberry in Australia 

 became a pressing subject for experiment. 



The germination of the teleutospores may be easily accomplished at the 

 proper season, either by placing them in a drop of water on a slide under 

 a bell-jar, or, better still, if copious germination is required, iby taking some 

 of the rusty straw and placing it on a drop or two of water in a petri dish, 

 the cover of which is lined with damp blotting-paper. It is only after a 

 considerable rest that they will germinate, and they start on warm days 

 about the end of September, which is the beginning of our spring. This 

 may continue through the warmer days of October, almost or entirely ceas- 

 ing in a cold spell, and even until November germination continues if the 

 conditions are favorable ; but although numerous trials have been made, no 

 germination has occurred outside these months. Generally speaking, the 

 middle of October is the height of the season for germination, and then, 

 too, the uredospores may be multiplying rapidly on the growing wheat- 

 plant ; so that there is no "off " season in Australia, as far as wheat is con- 

 cerned, when the teleutospores are active and the uredospores dormant, 

 In any case, as our wheat crops are usually harvested in November and 

 December, even if the barberry were common, and developed rust freely, 

 it could hardly be^of much importance as a factor in spreading the wheat 

 rust, since the aecidia would not be developed profusely before the wheat 

 crop had passed the danger point. 



The barberry is not a native of Australia, and very few hedges exist, 

 so that the question of its- infection is not of great immediate practical im- 

 portance, but it is of high scientific value to establish the fact that the rust 

 may pass one portion of its life on one plant, say, wheat, and continue it 

 on a very different plant as an intermediate host, say, barberry, and thus 

 settle that the rust with which we have to deal is the P zraminis of 

 Europe. 



As early as October, 1892, I succeeded in germinating the spores freely 

 and ^ copiously in a watch-glass with water, and infected four different 

 species of barberry obtained from the Botanic Gar'dens, two of which were 



