FUNGOID PESTS OF CULTIVATED PLANTS. 51 



CHRYSANTHEMUM RUST. 

 Uredo Chrysanthemi (Arth.), PL III. fig. 59. 



When this rust was first observed on the leaves of Chrysanthemum in 

 1897 it was believed that it would be discovered to be the Uredo form of 

 Puccinia Hieracii, and hence was called Uredo Hieracii ; but it has since 

 been shown that it must be regarded as a distinct species, for which no 

 teleutospores have yet been found. 



The pustules of the Uredo occur on the under side of the leaves, which 

 soon split irregularly and discharge the powdery snuff-coloured spores, 

 and these readily disperse themselves over the surface of the leaf. The 

 uredospores are somewhat elliptical, with a rough surface (17-32 x 16-36 /u), 

 and irregular in size. 



This pest at one time threatened to spread over France and this 

 country, and produce havoc amongst Chrysanthemums, but it has since 

 been brought under control. 



Spraying with potassium sulphide solution is recommended, especially 

 upon apparently clean leaves, while rusted leaves should be carefully 

 removed. Paraffin has also been recommended in dilution. 



It should be remembered that uncultivated composite plants are, of all 

 others, most susceptible to the attacks of rust and brand, and it is in that 

 direction that danger lies. 



Gard. Chron. Oct. 8, 1898, with figs. ; Mass. PL Dis. 241 ; Journ. 

 B.H.S. xxvi. 1902, p. 915 ; xxviii. 1904, p. 634 ; xxix. p. 769. 



Great trouble in the United States in growing Asters on account of 

 fungoid disease. (Journ. E.H.S. xxvi. 1901, p. 531.) 



CORN FLOWER BUST. 

 Puccinia Centaurece (DC.), PI. III. fig. 60. 



During the past year or two Corn flowers in cultivation have been 

 seriously attacked by this rust, which -has long been known on unculti- 

 vated species of Centaurea. 



We have nothing to do with the JEcidium here until it is proved to 

 be distinctly related to the rust on Cyanea. The Uredo appears on the 

 stem and leaves in elliptical pustules, which are longer on the stems , 

 soon fissured, and exposing the snuff-coloured uredospores which are 

 almost globose (22 JJL diam.), and we could detect no roughness on the 

 surface. The colour was pale brown under the microscope, and certainly 

 not, as some have stated, chestnut-brown. 



It is the custom in these latter days to lump together a number of the 

 species of rust found on composite plants under the name of Puccinia 

 Hieracii, and this among the number. For the present we prefer to 

 call it Puccinia Centaurece. 



We can only suggest the spraying of healthy plants, or those but 

 slightly affected, with the potassium sulphide solution and burning badly 

 diseased plants out of the way. 



Sacc. Syll. vii. 2210 ; Plowr. Brit. Ured. 186 ; Cooke M.F. 63, 207 ; 

 Journ. R.H.S. xxvi, 1901, p. cxxv. 



