CHAP, xin.] Fungoid Diseases of Trees 287 



Somewhat similar appearances of rust or blight are caused 

 by Caeoma laricis on the needles of Larch, and by C. abietis 

 pectinatae, and by Aecidium columnare on Silver Fir. 



3. Aecidium pint ^ Pers., var. adcola, the Pine needle-rust or 

 blight. 



During April and May, on the one and two-year-old 

 foliage of young Pine, minute orange-yellow blisters (Peridia} 

 are often to be seen in a row, either on one or both sides of 

 the needles, between which the Spermogonia lie. These turn 

 brown when mature, as also do the Peridia before they burst in 

 the middle and scatter their spores. The mycelium develops in 

 the inside of the needle without killing it, and again produces 

 Aecidia in the following year. The foliage is only killed off 

 and shed when the disease infects the plants extensively ; in 

 this case its marks may be traced by small, blackish, warty 

 spots with light edging. 



Although mainly confined to Pines (and in particular to Scots 

 and Black Pines) of from three to ten years of age, it may be 

 found in woods up to thirty years old, but always on needles of 

 the last or of former years, and never on the new flush of 

 foliage. Here again the formation of mixed in place of pure 

 woods, careful clearing and thinning, the removal of infected 

 twigs, and the removal of groundsel plants (species of Senecid] 

 on which the other generative form Coleosporium senetionis is 

 produced, constitute the only practical measures for obviating 

 the spread of the disease. 



Somewhat similar disorders are caused on one-year-old 

 Spruce foliage by A. abietinum. To one of the same genus, 

 A. strobilinum, is also due the fungoid disease common on the 

 bracts of Spruce cones. 



4. Trichosphaeria parasitica^ R. Hrtg., the Silver Fir needle- 

 blight. 



The thin, colourless mycelium is generally to be found on 

 the lower side of the last sprays of Silver Fir, whence it usually 

 attacks the needles pointing downwards, forming close white 



