50 THB VICTORIAN NATURALIST. 



considering the number of chrysanthemums that are imported. 

 It is interesting to note that many of the AustraHan-raised 

 varieties are less Uable to rust than others when grown in England 

 or America. 



Rose Rust, Phraginidium subcorticium Wint., is now very 

 common around Melbourne, particularly on the Sweetbriar, and 

 it has also become a pest in the nurseries, attacking seedlings in 

 a favourable season and killing them outright. It may have been 

 introduced in rose cuttings, smce the mycelium of the aecidium 

 is known to winter in the stem, and also with the seeds of the 

 Sweetbriar, which was among the first European plants to be 

 irnported into Tasmania and New South Wales and used as 

 hedges. 



Just to show in what unexpected ways rusts may be unwittingly 

 introduced, I may mention that both summer and winter spores 

 of the Wheat Rust, Puccinia graminis, have been found on 

 wheat-straw envelopes on bottles of wine imported from France. 



Hetercecism. — Variety seems to be the key-note of the life of 

 the rusts, for not only are the spore-forms very varied, as we 

 have seen, but in a number of species there is a further compli- 

 cation in different kinds of plants being selected by the same 

 rust for the formation of its various spores. In other words, one 

 part of its life is passed on one kind of plant, and the remainder 

 on a totally different species. And it will generally occur in the 

 struggle for existence that if two species compete against one 

 another for a host, the one that varies its host-plants will 

 probably succeed better than the other. It has a choice of food 

 and a change of diet, two very desirable things. 



This peculiarity of the rusts was first discovered by De Bary 

 in 1864, when he showed that rust in wheat produced its summer 

 and winter spores on wheat and its aecidial stage on the 

 Barberry. 



But here in Australia it is well known that there are no native 

 Barberries, and even Barberry hedges are scarce, so that while 

 the question was not of great practical importance to the 

 Australian wheat-growers, yet it was of great scientific interest to 

 establish the fact that this rust may pass one portion of its life 

 on one plant, and continue it on a very different plant as an 

 intermediate host, say, the Barberry. 



Accordingly, I infected several species of Barberry with 

 germinable spores of the rust, but without success, and in order 

 to give the experiment a trial under the most favourable con- 

 ditions, Dr. Plowright kindly sent me several young Barberry 

 bushes from England, which arrived here in good condition. 

 Some were infected by scattering rusty straw about the plants 

 and tying it on to them ; in other cases germinating spores were 

 applied direct to the leaves, and some were even planted at 



