DISEASE AND INSECTS 51 



FUNGOID DISEASES. 



Iris Rust. The only vegetable parasite which has 

 much obtruded itself upon the notice of the author is a 

 rust, Uredo Iridis, Thunb., and this is liable to be a very 

 serious pest of the Oncocyclus section. It is most un- 

 sightly, and though it does not kill the plants, it keeps 

 them in a more or less weak condition. It is easily 

 recognised, and if once introduced the only efficient 

 thing to be done, apparently, is to destroy the plants. 

 The pustules are described by Dr M. C. Cooke as linear- 

 ovate and sometimes confluent. They grow on both 

 surfaces, are covered at first by cuticle, and when 

 exposed, by its rupture, appear of a chestnut brown 

 colour. It is a British species and occurs sometimes on 

 Iris foetidissima but also occasionally on /. Pseudacorus. 

 It may not be uninteresting to point out that this fungus 

 is of the same genus as the " Rust" of wheat (Uredo 

 linearis), which is but one stage in a marvellous cycle of 

 changes. The yellow "Rust" of June and July becomes 

 the purple brown or almost black " Mildew " of autumn 

 (Puccinia graminis) and spores, 1 from this stage produce 

 the * ' Cluster-cups " (Aeadlurn Berberidis) on the leaves 

 of Barberry, from which again arises the Uredo form on 

 wheat. The point here to be noted, however, is that, 

 according to Dr Cooke, Uredo Iridis is supposed to be 

 without the Puccinia and Aecidium stages. The Uredo 

 Iridis is British, but it appears not unlikely that gardens 

 are troubled by an importation which is more virulent 

 than the native stock. 



Iris Bulb Scab. The next pest of consequence, 

 and the more serious in the fact that it may kill the 

 plant, is this Scab, caused by Mystrosporium adustum, 

 Mass. It affects Iris reticulata, and complaints of its 

 ravages have appeared in the gardening journals. An 



1 A spore is the analogue of a seed in flowering plants. 



