Uredospores. 2 1 



reaped at the end of spring, or beginning of summer in November and 

 December, so that it is the heat ajnd drought of summer, not the cold and 

 wet of winter, which the fungus has to provide against. In fact, the 

 wintering of the uredo is a misnomer here, for it is the excessive dryness 

 and heat which is most injurious. 



Bearing this in mind, it is easy to understand that P. graminis, although 

 it still continues to produce a certain amount of (teleutospores, is per- 

 petuated from season to season by means of uredospores. Self-sown 

 wheat or oats, or even the aftermath of either of these crops cut for hay, 

 is always more or less rusty during the late summer and autumn, the 

 uredospores being freshly produced then through the depth of winter. 



The teleutospores of P. graminis seem, unable to infect the barberry in 

 Australia, and this heteroecious rust would appear ito be fast becoming 

 like Uromyces fabae reduced to its lowest Kmits, and reproducing itself 

 only by uredospores. Of course the absence of the barberry would tend 

 to weaken if not destroy the capacity to produce the aecidial stage. 



Although the germination of uredospores during winter has already been 

 generally referred to, some definite instances may be given here, and 

 I will select those of Puccinia graminis, P. triticina, and P. chrysanthemi 

 from a number of tests made. The rust appeared on some self-sown 

 wheat, which Avas growing vigorously during winter ,(June), and on 

 placing the uredospores of P. graminis in a drop of water, they were 

 found to germinate sparsely in seventeen hours, and in twenty-one hours 

 they germinated freely and very generally. At the same time, and 

 from the same wheat plants, uredospores of P. triticina were placed under 

 similar conditions, and they also began to germinate within 21 hours, 

 but after several hours longer, only a few were germinating, and not too 

 luxuriously. 



The uredospores of P. chrysanthemi were also taken from green leaves 

 in May, and they germinated freely, producing long curved germ-tubes. 



Thus uredospores taken from growing plants during the winter are cap. 

 able of germinating, and this proves conclusively that self-sown, or 

 volunteer wheat, on the headlands or elsewhere in the neighbourhood of 

 growing crops is one of the means whereby rust may be continued from 

 season to season. In one case, which I have every reason to believe is 

 quite exceptional, the season's wheat, sown at Wellington, New South Wales, 

 in April, was badly rusted as early as May, but, as a general rule, it is 

 exceedingly difficult, even for the trained observer, to find more than an 

 odd speck of rust in a crop of wheat earlier than the end of September, 

 though there may be plenty on self-sown plants. 



There is a conflict of evidence, however, as to the conditions under 

 which germination takes place when the spores are not taken direct from 

 the fresh and growing plant. 



Eriksson (Eriksson and Henning 1 ) found that the uredospores of P. 

 graminis lost their capacity for germination during the winter if exposed 

 to the weather, but retained it if kept inside, and even then it gradually 

 disappeared, while Jacky 2 found that the uredospores of chrysanthemum 

 rust still retained their germinating power, after exposure to the weather 

 for 66 days, from ist December to 5th February. And Miss Gibson kept 

 spores of the same rust in a dry test-tube in a cool room for 7 1 days, from 

 March to May, and at the end of that time about one quarter germinated, 

 while a week after none germinated. 



The uredospore is primarily a spore for the rapid reproduction of the 

 species. As a rule, it is produced in immense numbers, it is provided 

 with a thin wall, having projections of some sort to act as a holdfast, and 

 it generally infests the leaf or sheath, so that nutrition is not directly 



