90 FUNGOID PESTS OF CULTIVATED PLANTS. 



The uredospores are paler than the teleutospores, irregularly rounded, 

 and rough (23-38 x 20-26 //). 



The teleutospores are comparatively large, elliptical in outline but 

 constricted in the middle, where they are divided into two cells. The 

 lower cell is a little narrowed into the pedicel, which soon falls 

 away. Externally the surface is smooth and of a dark brown colour 

 (30-56 x 17-28 p). 



The best plan is to eradicate all the plants as soon as the disease 

 makes its appearance, to prevent the germination of the teleutospores 

 and the dispersion of the rust. 



Sacc. Syll. vii. 2211 ; Cooke, Hdbk. No. 1493 ; Mass. Dis. PL 250 ; 

 Plowr. Brit. Ured. 156 ; Gard. Chron. May 13, 1905, p. 293. 



PARSNIP EOT MOULD. 

 Plasmopara nivea (Ung.), PL IX. fig. 114. 



This rot mould is similar in character and life-history to the other 

 rot moulds of which we have given an outline (Introduction, p. 2). It 

 first affects the leaves, and then the mycelium descends and forms resting 

 spores in the stems and roots. 



The white mouldy patches appear first on the under surface of the 

 leaves chiefly, forming an internal mycelium from which the bundles of 

 branched threads arise and appear on the surface. These threads are 

 erect, rather shorter than in many species (250 ^ long), tapering upwards 

 and mostly once or twice forked in the upper portion, rarely three-forked, 

 with from one to four horizontal branches near the apex, forked at the 

 extremity, with the forked spicules spreading, each point bearing a single 

 conidium or spore. These are nearly globose or ov,oid, with a very obtuse 

 projection or teat at the apex (20-25 x 15-17 yu), granular within and 

 with a slightly tawny tinge. It has also recently attacked Parsley 

 severely, see Gard. Chron. Nov. 5, 1904, p. 313. 



This mould has appeared in France, Belgium, Holland, Germany, 

 Sweden, Lapland, Tyrol, Italy, and N. America. 



Sacc. vii. 807 ; Smith, Field Crops, 239 ; Mass. B. F. 113, figs. 66-70; 

 Cooke M. F. ; Gard. Chron. Dec. 5, 1884, figs. 124, 125 ; Cooke, Hdbk. 

 No. 1775. 



CELERY SPOT MOULD. 

 Cercospora Apii (Fres.). 



This black mould is known throughout Europe and North America 

 on leaves of Celery and Parsnip causing leaf -spots which are at first 

 yellowish, then enlarging and turning brown. In this country it has not 

 yet been developed into a pest. 



Spots almost circular (4-6 mm. diam.) with the narrow margin 

 slightly elevated. The mould developed on the under surface in small 

 brown tufts. The hyphse, or threads, are either continuous or sometimes 

 with one or two divisions (40-60 x 4-5 ju). The conidia are thin, obclavate, 

 or attenuated upwards, with from three to ten transverse divisions 

 (50-80 x 4 p) almost colourless. 



The variety on Parsnip is knpwn in the United States and Siberia. 



