FUNGOID PESTS OF CULTIVATED PLANTS. 25 



The leaves are blistered and distorted, chiefly along the midrib, and 

 the petioles become swollen and gouty, usually twisted and pallid. Later 

 on these pustules split irregularly down the centre, and expose a mass of 

 blackish spores, like soot, which are scattered over the leaves. 



These spores are complex, like those of the smut on Hellebore and 

 Anemone, and consist of irregular rounded balls (82-50 x 20-45 /<) 

 compounded of a number of smaller cells, the central ones being dark 

 brown (10 x 17 /* diam.) and from one or two to six, angular by com- 

 pression, while the outer ones, or those of the circumference, are colourless 

 and somewhat hemispherical, but they do not germinate (6-10 ft diam.). 



When the coloured spores germinate they give origin to a short 

 thick thread (promycelium) into which the coloured contents of the spore 

 pass. From the end of this thread five or six fusiform secondary spores 

 are produced. Sometimes the secondary spores will germinate and 

 produce tertiary spores. 



This parasite is so deeply seated that fungicides are of little avail. 

 All that can be done is to pick off all the diseased leaves, as soon as they 

 appear, and burn them, so as to prevent the germination of the spores 

 and the spreading of the disease. 



It is certainly well known in France, Germany, and Italy. 



Sacc. Syll. vii. 1905 ; Cooke M. F. 92, 232, t. ix., f. 185, 186 ; Mass. 

 B. F. 189 ; Plowr.Brit. Urea 1 . 288 ; Cooke Hdbk. No. 1538 ; Tubeuf, Dis. 

 317. fig. 174 ; Gard. Chron. Sept, 30, 1876. 



Violet Rust. 

 Puccinia Viola (Schum.), PL I. fig. 20. 



The Violet rust is so widely diffused, and so general on wild plants, 

 that it is fortunate it is not found oftener in the garden than it is. Like 

 many others of its kindred it is developed under three forms or stages, 

 the earliest being the cluster-cups, and afterwards the Uredo and the 

 Puccinia. For practical purposes it is better to treat them as distinct 

 diseases, without reference to their genetic connection, or, at least in so 

 far as the cluster-cups are concerned, their entirely different appearance 

 to the ordinary observer. The pustules of the Uredo, and afterwards of 

 the Puccinia, are scattered over the surface of the leaves, the former of a 

 rusty-brown colour, and the latter dark brown, nearly black, breaking 

 through the epidermis. 



The uredospores are powdery, and are produced in little pustules on 

 either surface of the leaves. Individually they are nearly globose, and 

 rough with short spines (21-26 x 17-23 ju). 



The teleutospores, or final spores, are darker in colour, and are pro- 

 duced in similar pustules, often mixed with those of the Uredo. They 

 have the usual Puccinia form, with a central partition dividing them into 

 two cells (20-35 x 15-20 fi). 



When mature these teleutospores are capable of germinating from 

 each cell, the threads so produced developing towards their apex two or 

 three secondary spores, which are simple and much smaller than the 

 primary spore. The life-history and development are very similar in all 

 the species of Puccinia. See Introduction, p. 5. 



