164 TRANSACTIONS OF THE [Skss. 



PUCCINIA MIRABILISSIMA, PeCK, A NeW BrITISH ReCORD. 



By Malcolm Wilson, D.Sc, F.R.S.E., Reader in 

 Mycology, University of Edinburgh. 



(Read 16th November 1922.) 



The occurrence in the vicinity of Edinburgh of Puccinia 

 mirabilissmia, a species hitherto only recorded from the 

 Unites States of America, is a somewhat surprising circum- 

 stance. Up to the present this rust has been found in Utah, 

 Montana, Colorado, and in the Sierra Nevada Mountains,^ and 

 there is a single record from Washington.^ The fungus 

 usually occurs on Berberis repens, but has also been found on 

 B. pinnata, B. nana, B. pumila, and B. Aquifolia, species 

 which are all included in the sub-genus Malionia. It was first 

 collected at Colinton near Edinburgh in October 1922 on 

 B. Aquifolia, and has later been found on the same host at 

 Newlands, Peeblesshire. 



The fungus produces its small reddish sori abundantly on the 

 under surface of the leaf, the attacked plants being rendered 

 very conspicuous by the development of bright red spots on 

 the upper leaf surface opposite to the fructifications. Up 

 to the present only uredospores and teleutospores have been 

 found, and these occur in the same sori. It is still doubtful 

 whether any other spore stage is produced by the fungus, for 

 though aecidia have been described on B. repens in the United 

 States, the specific connection between these and the uredo- 

 spores and teleutospores has not been proved. 



The cushion-shaped almost hemispherical sori are made up 

 of a large number of uredospores, intermingled with which 

 are a few teleutospores. The uredosj)ores possess long colour- 

 less pedicels which radiate out from the centre and form the 

 bulk of the compact sorus. The uredospores are attached to 

 these by a distinct articulation, and only separate at maturity, 

 leaving the pedicels still in the sorus (fig. 1, p. 166). The spores 

 are obovate or pyriform, with finely rugose wall, averaging 

 30 X 18 /A. Each possesses 2-4, usually 3, equatorially arranged 



' Blasdale, W. C. : Observations on Puccinia mirahilissima. Erythea, 

 vol. iii, 1895, p. 1.31. 



2 Plant Disease Survey, Supp. 2.3, 1922. Bur. Plant Industry, Dept. 

 Agrie. U.S.A. 



