FUNGOID PESTS OF FOKEST TREES. 



367 



No suggestion can be offered to check this parasite, from which many 

 healthy trees constantly escape. Recorded throughout Europe and in 

 North America. 



Sacc. Syll. iii. 3138 ; Cooke, Hdbk. No. 1297 ; Grevillca, xiv. 105. 



A leaf-spot, caused by Asteroma ulmi (Klotsch), has been recorded on 

 Elm leaves in Britain, France, and Portugal, but the fruit does not appear 

 to be known. 



Cooke, Hdbk. No. 1369. 



Elm-Leaf Scab. 

 Piggotia astroidea (Berk.), PI. XIX. fig. 13. 



Berkeley first made known the details of the structure cf this parasite, 

 and applied to it the name which it now bears. It occurs on the upper 

 surface of living Elm leaves as small blackish scabs formed from the 

 aggregation of minute tubercles, clustered in a stellate manner, and at 

 first covered by the cuticle. The tubercles or receptacles are flattened, 

 thin, and dark olive. The conidia are oblong, truncate at the base, and 

 rounded at the apex (8-10 x 5-6 /u), containing from two to four minute 

 guttules, and generated at the apex of short pedicels which are fasciculate. 



The presumed phases, or stages, in the life-history of this fungus, are 

 recorded in the following note on the " Elm-leaf blotch." 



Sacc. Syll. iii. 3387; Cooke, Hdbk. No. 1296; Berk. A. N.H. 

 No. 503, t. v. f . 3 ; Grevillea, xiv. 106. 



Elm-leaf blister, caused by Taphrina ulmi (Joh.), occurs on leaves 

 of Common Elm, and Wych Elm, but is doubtfully British. 

 Mass. PI. Dis. p. 92. 



Elm-Leaf Blotch. 

 Phyllachora ulmi (Fckl.), PI. XIX. fig. 14. 



This blotch is not unusual on Elm leaves, which is supposed to pass 

 through three stages, all of which have been recognised as different and 

 distinct parasites, but are now assumed to be three conditions of the same 

 species. The first stage, which has been termed the spermogonia, is still 

 generally known as Phlozospora ulmi. The second stage, called the 

 pycnidia, is known as Piggotia astroidea, both of which have been 

 described here as different diseases. And the last is the perfect Phylla- 

 chora ulmi, in which the spores are produced in asci, and become matured 

 on the dead leaves after remaining upon the ground. 



The blotches are rounded, convex, nearly black, and somewhat rough 

 on the surface, on the upper face of the leaves. Within these excrescences 

 are white cavities or cells, in which the fructification is produced. Numerous 

 cylindrical sacs or asci (60-70 x 8 /j) are developed, side by side, each 

 enclosing eight oblong, colourless, sporidia (10-11 x 5 /u), which are 

 extruded, when mature, through an opening at the apex cf the cell. The 

 stroma or blotch is greyish after maturing upon the ground. 



