Galls caused by the fungus Polycystis violae Brem 



on 



the leaf-stalks of Viola oanina Linn. 

 PLATE 100. 

 Synonymy of Fungus. 



Urocystis violce Br. 



Popular Name of the Fungus. 

 The Violet-smut Cooke. 



Habitat of the Dog-violet.— Freely distributed through- 

 out the whole of Britain in woods, thickets, by streams, on 

 hedge-banks, and other open, dry, or sandy situations. 



The Gall is formed by the rapid and enormous multipli- 

 cation of the spores of the fungus within the tissues of 

 the plant. 



Position.— On the leaf-stalk. 



Manner of Growth. — Singly, usually ; seldom more than 

 four on one stalk ; glabrous, glossy. 



Colour. — Green, reddish, purple. 



Average Dimensions of a Mature Specimen. 

 Length, 40 mm.; greate.st girth, 18 mm. 



May be sought during the months of April, May, and June. 



The Growth is complete by the end of June. 



These swellings are very similar to those on Ranunculus 

 repens, but are more extensive and, in proportion to the thick- 

 ness of the leaf-stalk, are much larger. In some specimens the 

 leaf is dwarfed considerably in size ; in others it is not materially 

 affected, even though the mid-rib may be swollen as greatly as 

 the stalk to which it is attached. During the growth of the 

 fungus the swellings are hard. There are seldom more than 

 four separate swellings on a leaf-stalk, the length of which is 

 usually about 100 mm. 



The gall is also figured by Cooke, " Rust, Smut, Mildew, 

 and Mould," plate 9. 



The illustration is of specimens gathered at Battle by the 

 author. 



232 



